32nd International Symposium on Lattice Field Theory (Lattice 2014)

23 Jun 2014, 08:00 → 28 Jun 2014, 18:00 US/Eastern

Columbia University

Norman Christ (Columbia University)

The 32nd International Symposium on Lattice Field Theory will be held at Columbia University, New York from Monday, June 23 to Saturday, June 28, 2014. The Symposium will be organized jointly by Brookhaven National Laboratory and Columbia University. For further details, please refer to http://www.bnl.gov/lattice2014.

Monday, 23 June

Plenary

Convener: Prof. Zoltan Fodor (University of Wuppertal)

1 Conference opening

2 Hadron Structure

Speaker: Dr Martha Constantinou (University of Cyprus)

Slides talk_MConstantinou.pdf

3 Heavy Flavors

Speaker: Chris Bouchard (The Ohio State University)

Slides Bouchard_LAT14.pdf Bouchard_LAT14.pptx

10:45 Coffee Break

Plenary

Convener: Prof. Gernot Münster (University of Muenster)

4 Recent results on topology on the lattice (in memory of Pierre van Baal)

Speaker: Prof. Michael Mueller-Preussker (Humboldt-Universitaet zu Berlin)

Slides plen_talk_topology_MMP_v3.pdf

5 Finite Temperature (\mu=0)

Speaker: Alexei Bazavov (University of California/University of Iowa)

Slides bazavov_lat14.pdf

Algorithms and Machines: Parallel 1F

Convener: Dr Mike Clark (NVIDIA)

6 Dynamical QCD+QED simulation with staggered quarks

Electromagnetic effects play an important role in many phenomena such as isospin symmetry breaking in the hadron spectrum, hadronic contributions to g-2, etc. We have generalized the MILC QCD code to include the electromagnetic field. In this work, we focus on simulations including charged sea quarks using the RHMC algorithm. We explain the algorithm, code performance, and results for some observables.

Speaker: Dr Ran Zhou (Fermilab)

Slides Ran.QCDQED.pdf

7 Application of Adaptive Multigrid Algorithm in Hybrid Monte Carlo Simulations

Lattice QCD has entered the era of simulations directly at the physical quark masses thanks to the increasing computing power and algorithmic advancement. But the computational cost for such simulations is still extremely high, both for the gauge field generation and the measurements of physical observables. Adaptive multi grid (MG) algorithm has proven to be quite effective in reducing the computational cost in measurements with Wilson-type fermions, provided that many measurements are performed on one gauge configuration due to the high setup cost for MG. We explore the feasibility of applying the multi grid algorithm in the hybrid Monte Carlo simulations with Wilson fermions, and show some preliminary results.

Speaker: Dr Meifeng Lin (Brookhaven National Laboratory)

Slides LAT2014_MLin.pdf

8 Diffusion of topological charge and scaling of autocorrelation times in hybrid Monte Carlo simulations of lattice QCD

We determine the scaling behavior of the autocorrelation times of observables constructed from the topological charge density on lattices with periodic and open boundary conditions using a series of high-statistics numerical simulations. The autocorrelation functions of such observables turn out to obey a simple differential equation which allows the motion of topological charge in hybrid Monte Carlo simulations to be understood in terms of only two processes: diffusion and tunneling. There is a characteristic lattice spacing at which open boundary conditions become worthwhile for reducing autocorrelations and we show how this lattice spacing is related to the diffusion constant, the tunneling rate, and the lattice Euclidean time extent.

Speaker: Mr Greg McGlynn (Columbia University)

Slides talk.pdf

9 Multigrid Preconditioning for the Overlap Operator

The overlap lattice discretization of the Dirac operator preserves the important physical property of chiral symmetry, at the expense of requiring much more effort when solving systems with this operator. We present a preconditioning technique based on another lattice discretization, the Wilson-Dirac operator. Recently, close to normal operators have gained popularity in numerical simulations. Therefore, we give a mathematical analysis which shows that our preconditioner is effective in an idealized setting where operators are assumed to be normal. This is then confirmed by numerical experiments which are performed for large lattice configurations coming from state-of-the-art physical simulations, implemented on a parallel cluster computer with up to 8,192 cores.

Speaker: Mr Matthias Rottmann (University of Wuppertal)

Slides rottmann_lattice14.pdf

10 The FUEL code project

I will give an introduction to the FUEL project for lattice field theory code. The code being developed (called "qhmc") was initially targeted for gauge field generation for beyond standard model theories, and is now growing into a more general framework suitable for analysis too. The design is based on using the Lua scripting language as a wrapper for existing lattice field theory libraries, which provides a quick and easy way to develop new calculations. The implementation currently only supports the USQCD QOPQDP and QDP/C libraries, with support for other optimized libraries planned. I will discuss the current status of the code along with future plans for development.

Speaker: James Osborn (ANL)

Slides talk.pdf

Chiral Symmetry: Parallel 1G

Convener: Prof. Artan Borici (Uiversity of Tirana)

11 Phase Diagram of Wilson and Twisted Mass Fermions at finite isospin chemical potential

A finite lattice spacing may have a crucial impact on the phase diagram of QCD. The existence of the Aoki phase for Wilson fermions underlines this point. Sharpe and Wu already showed that this kind of lattice artifacts carry over to finite twisted mass. The next task is the calculation of the phase diagram at finite chemical potential. I will present the phase diagram of Wilson fermions of two-flavor QCD at finite twist as well as at finite iso-spin chemical potential. Thereby the order parameters of the new phases are pointed out and the pion masses are presented.

Speaker: Dr Mario Kieburg (University Bielefeld)

Slides LATTICE_2014_Kieburg.pdf

12 Phase diagram of non-degenerate twisted mass fermions

In this talk, I will summarize recent work with Prof. Stephen Sharpe in mapping out the phase diagram and pion spectrum for chiral perturbation theory with twisted-mass fermions in the presence of non-degeneracy between the up and down quark and discretization errors. I will show how the CP-violating phase of the continuum theory, which occurs for sufficiently large non-degeneracy, is continuously connected to the Aoki-phase found in the lattice theory with degenerate quarks. Both for the Aoki-phase and first-order scenarios, this results in a critical surface along which at least one of the pions is massless. In the pion spectrum, I will focus mainly on the maximal twist case, where there is competition between the effects of non-degeneracy and twist-dependent discretization errors, resulting in a complete breakdown of isospin symmetry with all three pions having different masses. This breakdown of isospin symmetry should be a useful indicator of the size of discretization errors as simulations with twisted-mass fermions move to non-degenerate masses. Lastly, I will show numerical results for the effects of higher order terms on the phase diagram and the pion spectrum.

Speaker: Derek Horkel (University of Washington)

Slides Phase Diagram of Non-Degenerate Twisted Mass Fermions

13 Individual eigenvalue distributions for chGSE-chGUE crossover and determination of low-energy constants in two-color QCD+QED

We evaluate the individual distributions of four smallest eigenvalues from chiral random matrix ensembles interpolating chGSE and chGUE by the quadrature method applied to the Fredholm Pfaffian of dynamical Bessel kernel containing a crossover parameter. These distributions are then fitted with the staggered Dirac spectra of the quenched SU(2) lattice gauge theory in the presence of fluctuating or constant U(1) fields. Combination of the four best-fitting crossover parameters from matching each random matrix theory prediction to the corresponding histogram of the k-th Dirac eigenvalue allows for an efficient and precise determination of low-energy constants F and \Sigma in the chiral Lagrangian of Nambu-Goldstone bosons on the coset space SU(2n)/Sp(2n) from relatively small lattices.

Speaker: Dr Shinsuke M. Nishigaki (Shimane University)

Slides Nishigaki.pdf

14 Mesons upon low-lying Dirac mode exclusion

We study the iso-scalar and iso-vector mesons under the exclusion of the low-lying Dirac modes from valence quarks with the overlap operator within the two flavour lattice QCD. We study mesonic correlators and extract states at each level of such low-mode truncation. Our observations support a simultaneous restoration of both SU(2)_L \times SU(2)_R and U(1)_A symmetries. We finally observe a degeneracy of all isovector and isoscalar J=1 mesons that serves as an indication of some higher symmetry in the chirally restored regime.

Speaker: Mr Mikhail Denissenya (University of Graz)

Slides DenissenyaLat2014.pdf

15 Fine lattice simulations with the Ginsparg-Wilson fermions

We report the status of 2+1-flavor simulations with the Mobius domain-wall fermions on fine lattices of 1/a = 2.4 and 3.6 GeV. The violation of the Ginsparg-Wilson relation is controlled at the level of 0.5 MeV or better. Analyses of the Wilson flow observables, heavy quark potential and light-hadron correlator are presented.

Speaker: Dr Junichi Noaki (KEK)

Slides latt2014_noaki.pdf

Hadron Structure: Parallel 1D

Convener: Marina Marinkovic

16 A new strategy for evaluating the LO HVP contribution to (g-2)_mu on the lattice

We propose a hybrid strategy for the lattice evaluation of the leading order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon. The strategy combines direct numerical integration of lattice data for Q^2 greater than Q^2_min with the use of fit forms to handle the lattice data in the low-Q^2 region Q^2 less than Q^2_min. Using a physical model for the I=1 subtracted vector polarization, constructed from experimental data, we study the systematics of this strategy, determining how low a choice of Q^2_min is possible for current lattice simulations, and identifying three types of fit forms whose use in the low-Q^2 region will lead to results with systematic uncertainties well below the 1% level.

Speaker: Kim Maltman (York University, Toronto)

Slides krm_latt2014_gminus2.pdf

17 The leading hadronic contribution to (g-2) of the muon: The chiral behavior using the mixed representation method

We extend our analysis of the leading hadronic contribution to the anomalous magnetic moment of the muon using the mixed representation method to approach the physical point. We present results derived from local-conserved two-point lattice vector correlation functions, computed on a subset of light two-flavor ensembles made available to us through the CLS effort with pion masses as low as 190MeV. The data is analyzed also using the more standard four-momentum method. Both methods are systematically compared as the calculations approach the physical point.

Speaker: Dr Anthony Francis (Helmholtz-Institut Mainz)

Slides afrancis-lattice2014.pdf

18 The leading disconnected contribution to the anomalous magnetic moment of the muon

The hadronic vacuum polarization can be determined from the vector correlator in a mixed time-momentum representation. We explicitly calculate the disconnected contribution to the vector correlator, both in the $N_f = 2$ theory and with an additional quenched strange quark, using non-perturbatively $O(a)$-improved Wilson fermions. All-to-all propagators are computed using stochastic sources and a generalized hopping parameter expansion. Combining the result with the dominant connected contribution, we are able to estimate an upper bound for the systematic error that arises from neglecting the disconnected contribution in the determination of $(g-2)_\mu$.

Speaker: Ms Vera Guelpers (University of Mainz)

Slides guelpers_lattice2014.pdf

19 The strange and charm quark contributions to the anomalous magnetic moment (g -2) of the muon from current-current correlators

We describe a new technique (presented in arXiv:1403.1778) to determine the contribution to the anomalous magnetic moment (g-2) of the muon coming from the hadronic vacuum polarization using lattice QCD. Our method uses Padé approximants to reconstruct the Adler function from its derivatives at q^2=0. These are obtained simply and accurately from time-moments of the vector current-current correlator at zero spatial momentum. We test the method using strange quark correlators calculated on MILC Collaboration's n_f = 2+1+1 HISQ ensembles at multiple values of the lattice spacing, multiple volumes and multiple light sea quark masses (including physical pion mass configurations).

Speaker: Ms Bipasha Chakraborty (SUPA, School of Physics and Astronomy, University of Glasgow)

Slides Chakraborty_Lattice2014.pdf

20 Lattice Calculation of the Hadronic Light by Light Contributions to the Muon Anomalous Magnetic Moment

The anomalous magnetic moment of muon, g-2, is a very precisely measured quantity. However, the current measurement disgrees with standard model by about 3σ. Hadronic vaccum polarization and hadronic light by light are the two types of processes that contribute most to the theorectial uncertainty. We will discuss the light by light lattice calculation and some strategies of including QED on lattice.

Speaker: Mr Luchang Jin (Columbia University)

Slides lattice2014.pdf

Hadron spectroscopy and interaction: Parallel 1B

Convener: Prof. Sinya Aoki (Yukawa Institute for Theoretical Physics, Kyoto University)

21 Pion-pion scattering phase shifts with the stochastic LapH method

Progress in calculating scattering phase shifts on Nf=2+1 anisotropic clover Wilson lattices is described. The stochastic LapH method facilitates computations in large volumes and for light pion masses. Results for pion masses down to 250 MeV, keeping m_pi L > 4, are presented.

Speaker: Mr Brendan Fahy (Carnegie Mellon University)

Slides BrendanFahy_lattice2014.pdf

22 Pi-Pi Scattering with N_f=2+1+1 Twisted Mass Fermions

Pi-Pi scattering is investigated for the first time for N_f=2+1+1 dynamical quark flavours using Wilson twisted mass fermions. Lüschers finite size method is used to relate energy shifts in finite volume to scattering quantities like the scattering length in the I=2 channel. The computation is performed at several pion masses and lattice spacings utilysing the stochastic LapH method, which is applied to spatial lattice volumes as large as 48^3.

Speaker: Dr Bastian Knippschild (HISKP, University Bonn)

Slides Lattice2014_Knippschild.pdf

23 Lattice study of pion-pion scattering using Nf=2+1 Wilson improved quarks with masses down to their physical values.

for the BMW Collaboration. We use 2HEX smeared gauge configurations generated with the Nf=2+1 clover improved Wilson action to investigate pion-pion scattering in the rho channel. The range of lattice spacings (0.054 fm to 0.12 fm) and space-like extents (32 and 48) allows us to extract the scattering parameters through the volume dependence of the effective mass according to Luscher's formalism. In particular, we consider bases of up to 5 operators to extract these levels. Our pion masses, down to 134 MeV, allow us to begin studying the light-quark-mass dependence of the resonance parameters.

Speaker: Mr Thibaut METIVET (CEA Saclay)

Slides Lattice2014Talk.pdf

24 K-pi scattering lengths at physical kinematics

I will present preliminary results on K-pi scattering lengths obtained by the RBC-UKQCD collaboration. The results are obtained using one of our domain wall fermion ensembles with physical quark masses. I will argue that the large "around-the-world" effects which are present with such light quark masses can be controlled.

Speaker: Mr Tadeusz Janowski (University of Southampton)

Slides kpiscattering.pdf

25 Resonances in pi-K scattering

We have obtained clear signals of resonances in coupled-channel pi K - eta K scattering. Using distillation and a large basis of operators we are able to extract a precise spectrum of energy levels using the variational method. These energies are analysed using inelastic extensions of the Luescher method to obtain scattering amplitudes that clearly describe S, P and D wave resonances, corresponding to the physical K_0^*(1430), the K^*(892) and the K_2^*(1430).

Speaker: Dr David Wilson (Old Dominion University)

Slides DavidWilson_Lattice2014.pdf

Nonzero temperature and Density: Parallel 1A

Convener: Shinji Ejiri

26 Curvature of the QCD critical line with 2+1 HISQ fermions

We present results on the curvature of the critical line of QCD with 2+1 HISQ fermions at nonzero temperature and quark density obtained by analytic continuation from imaginary chemical potentials. Monte Carlo simulations are performed by means of the MILC code suitably modified to include a nonzero imaginary baryon chemical potential. We set the chemical potential at the same value for the three quark species, and we work on a line of constant physics with a light to strange mass ratio of 1/20.

Speaker: Dr Leonardo Cosmai (INFN)

Slides talk_Cosmai.pdf

27 The curvature of the QCD critical line from analytic continuation

We present preliminary results regarding the curvature of the critical line of N_f = 2+1 QCD with physical quark masses. We make use of the stout improved staggered fermions formulation, with a tree level improved Symanzik gauge action.

Speaker: Michele Mesiti (University of Pisa & INFN)

Slides lattice2014.pdf

28 Phase diagram of QCD at finite isospin chemical potential with Wilson fermions

We investigate the structure of the phase diagram of QCD at finite isospin chemical potential with Wilson fermions. From the behavior of meson correlators in temporal and spatial directions, Polyakov loop, isospin density and susceptibilities as a function of isospin chemical potential at zero and finite temperature, we extract the QCD phases at finite isospin chemical potential and temperature. We make comparison among our results, previous studies with effective theories, lattice QCD with KS fermions and high density QCD with heavy quark limit.

Speaker: Prof. Chiho Nonaka (Nagoya University)

Slides lattice2014_nonaka.pdf

29 QCD with Wilson fermions and isospin chemical potential at finite and zero temperature

We study QCD with Wilson fermions in the presence of an isospin chemical potential mu_I. At zero temperature, condensation of iso-positive pions is expected to occur as soon as mu_I reaches half the pion mass. By looking at the isospin density and the mass spectrum of mesons as a function of mu_I, we investigate this pion condensation on the lattice and extend the study to non-zero temperature. By increasing mu_I further, we also look for a possible condensation of additional mesons and for a saturation transition.

Speaker: Mr Tobias Rindlisbacher (ETH Zurich)

Slides lattice2014.pdf

30 Status of the SU3 Lambda Scale

We compare the non-perturbative SU(3) lambada scale of Necco and Sommer with the lambda scale derived by Bazavov et al. from deconfining phase transition data of the Bielefeld group and others. Though the relative discrepancy is never larger than 2%, it matters in some applications. Differences are encountered between results from the set of smaller lattices of Necco and Sommer and pseudo-deconfining temperatures on similarly sized lattices, while their set of less accurate calculations on larger lattices is consistent with either of the results from smaller lattices. In conclusion, more accurate calculations on large lattices are desirable.

Speaker: Prof. Bernd Berg (Florida State University)

Slides Lat14.pdf

Nonzero temperature and Density: Parallel 1E

Convener: Christof Gattringer

31 Chiral restoration and deconfinement in two-color QCD with two flavors of staggered quarks

We study chiral restoration and deconfinement in two-color QCD with two flavors of staggered quarks using a RHMC algorithm on GPUs. We measure the chiral condensate and the corresponding chiral susceptibility over the lattice coupling across the finite temperature transition. Using Ferrenberg-Swendsen reweighting we extract the maxima of the chiral susceptibility in order to determine pseudo-critical couplings on various lattices suitable for chiral extrapolations. These are then used to fix the relation between coupling and temperature in the chiral limit, and to extract the critical exponents for magnetic scaling.

Speaker: Mr David Scheffler (TU Darmstadt)

Slides slides_opt.pdf

32 Effective SU(2) Polyakov Loop Theories with Heavy Quarks on the Lattice

We compare SU(2) Polyakov loop models with different actions with data from full two-color QCD simulations around and above the critical Temperature [1,2]. We then apply the effective theory at finite temperature and density to extract quantities like Polyakov loop correlators, effective Polyakov loop potentials and baryon density. [1] Smith et al. , Phys. Rev. D88 (2013) 054020 [2] Scheffler et al. , arXiv: 1311.4324

Speaker: Mr Philipp Scior (TU Darmstadt)

Slides scior.pdf

33 The effective Polyakov loop theory for finite temperature Yang-Mills theory and QCD

The effective Polyakov loop theory reproduces the main features of the Yang-Mills theory and QCD at finite temperature. A systematic derivation of the effective theory is a combined strong coupling and hopping parameter expansion. It includes a systematic ordering principle of the effective couplings. I will review this approach as well as results and possible applications. Furthermore, I will discuss how non-perturbative corrections to the couplings can be derived from simulations of the full theory.

Speaker: Dr Georg Bergner (ITP Goethe University Frankfurt)

Slides 14VortragLattice.pdf

34 Lattice simulations of G2-QCD at finite density I

In G2-QCD the SU(3) gauge group of QCD is replaced by the exceptional Lie group G2. This replacement leads to a theory that does not have a sign problem and can be simulated at finite baryon density using standard lattice techniques. The price to pay is that it contains bosonic as well as fermionic baryons. The physics of the light bosonic baryons is expected to be analogous to other QCD-like theories without sign problem such as two-color QCD or QCD with adjoint quarks. As adjoint QCD, it also contains fermionic baryons such as nucleons and deltas to form G2-nuclear matter while it is known from quenched simulations that it resembles QCD more closely than adjoint QCD does. We review the properties of G2-QCD, our results on its baryon spectrum, and how the observed mass hierarchy in this spectrum is reflected in the baryon density at finite chemical potential.

Speaker: Prof. Lorenz von Smekal (TU Darmstadt and JLU Giessen)

Slides LvS.pdf

35 Lattice simulations of G2-QCD at finite density II

G2-QCD is a QCD-like theory with fermionic baryons and fundamental quarks. Unlike QCD it does not suffer from a fermion sign problem at finite baryon density and therefore allows to investigate effects of fermionic baryons on the G2-QCD phase diagram with standard Monte-Carlo methods. In the talk we present recent results on the phase diagram at zero and non-zero temperature with an emphasis on Chiral- and Diquark-Condensation. We discuss various transitions in the quark number density related to the observed mass hierarchy in the spectrum and show evidence for a first order nuclear matter transition.

Speaker: Dr Bjoern Wellegehausen (JLU Giessen)

Slides document.pdf

Physics beyond the standard model: Parallel 1C

Convener: Biagio Lucini

36 Models of Walking Technicolor on the Lattice

We perform lattice simulations gauge theories with fermions in non-fundamental representations of the gauge group, which might be models for Walking Technicolor theories. In particular we update results reported earlier on SU(3) gauge theory with colour-sextet quarks. In addition we will report on results (if any) obtained for SU(2) gauge theory with colour-adjoint fermions.

Speaker: Dr Donald Sinclair (Argonne National Laboratory)

Slides 1-Sinclair.pdf

37 Phase Structure Study of SU(2) Lattice Gauge Theory with 8 flavours

We present the phase structure for SU(2) lattice gauge theory with 8 flavours of staggered fermions in the fundamental representation. One bulk phase transition is observed through the measurement of the plaquette, smeared Polyakov loops, as well as the Dirac operator eigenvalue spectrum. To further identify the order of the bulk phase transition pertaining to confinement and deconfinement, we resort to cold-start and hot-start simulations and the study of the constraint effective potential relating to distributions for smeared Polyakov loops.

Speaker: Ms Cynthia Yu-Han Huang (National Chiao-Tung University, Taiwan)

Slides lattice2014.pdf

38 SU(2) gauge theory with many flavors of domain-wall fermions

We numerically study the SU(2) gauge theory with many flavors. Dynamical simulation is performed with the standard domain-wall fermions in fundamental representation at numbers of flavors Nf=2,4,6, and 8. Nf dependence of the static potential, meson spectrum, and the eigenvalue spectrum of the Dirac operator is investigated so as to determine the phase structure.

Speaker: Dr Hideo Matsufuru (High Energy Accelerator Research Organization (KEK))

Slides lattice_2014.pdf

39 Approaching Conformality

We discuss our results on the thermal phase transition in color $SU(3)$ QCD with a large number $N_f$ of fundamental fermions using lattice gauge theory. We study the dependence of the critical temperature $T_c$ of the transition and of the coupling at $T_c$ on $N_f$. These results are used to investigate precursory effects of conformality associated with the emergence of a non-trivial fixed point at large $N_f$ and to show how real quark gluon plasma is smoothly connected to a strongly coupled system at zero temperature.

Speaker: Mr Tiago Jose Nunes da Silva (University of Groningen)

Slides Lattice-2014.pdf

40 Walking technicolor: testing infra-red conformality with exact results in two dimensions

We study two exactly solvable conformal models, the critical 2d Ising model and the Sommerfield model on the lattice. We find that some conditions on the geometry of the lattice must be fulfilled in order to obtain results free of systematic errors. In the Sommerfield model we also introduce a mass deformation and measure the mass anomalous dimension, $\gamma_m$. We find that the explicit scale breaking of the lattice induces corrections which have to be taken into account in order to reproduce $\gamma_m$ at the infrared fixed point. These results can be used to improve the methodology in the search for the conformal window in QCD-like theories with many flavors.

Speaker: Mr Oscar Akerlund (ETH Zurich)

Slides talkLatt14_short.pdf

15:55 Coffee Break

Algorithms and Machines: Parallel 2F

Convener: James Osborn (ANL)

41 CLS 2+1 flavor simulations

We report on the status of large volume simulations with 2+1 dynamical quarks which are being performed by the CLS collaboration. The algorithmic details include: open boundary conditions, twisted mass reweighting and the rational approximation for the strange quark, whereas the main feature of the simulation strategy is the approach to the physical point along a trajectory of constant trace of the mass matrix. We comment on the practical side of the above issues using as examples some of the newly generated ensembles, which presently cover lattice spacings between 0.11 fm and 0.05 fm and pion masses between 415 MeV and 150 MeV.

Speaker: Dr Piotr Korcyl (DESY Zeuthen)

Slides lattice2014.pdf

42 Adaptive Multigrid Solvers for LQCD on GPUs

There has been much progress to date in developing scalable sparse linear solver algorithms on GPUs, utilizing well-known mathematical methods such as mixed precision, domain decomposition and pipelining to improve performance, allowing efficient use of large GPU installations such as Blue Waters and Titan. However, there has been less focus on deploying 'mathematically optimal' linear solvers, that have optimal O(N) complexity. In this work we utilize the QUDA framework to deploy adaptive multigrid solvers on GPUs, in particular we describe the architecture abstractions that allow for deployment on heterogeneous systems, utilizing both GPUs and CPUs. We discuss in general the suitability of heterogeneous architectures for hierarchical algorithms, and compare performance against a highly optimized CPU implementation.

Speaker: Dr M Clark (NVIDIA)

Slides lattice_2014.pdf

43 Extending the QUDA library with the EigCG solver

Realization of the Incremental eigCG algorithm for solving Hermitian linear systems with multiple right hand sides on the CUDA platform is reported. In particular, we present details of implementation of the algorithm in the QUDA library. Preliminary performance results are provided.

Speaker: Dr Alexei Strelchenko (Fermilab)

Slides quda-eigcg-latt2014.pdf

44 Achieving strong scaling in many-GPU calculations in lattice QCD

We describe recent additions to the QUDA software library that are aimed at extending strong scaling in multi-GPU lattice calculations. These include the addition of CPU-thread support in order to increase concurrency and improve the overlap of computation and communication in Krylov solver routines, as well as the modifications needed to enable the GPUDirect RDMA feature recently introduced by NVIDIA and Mellanox. However, we focus in particular on the implementation and performance of so-called S-step variants of common Krylov solvers on current NVIDIA hardware. The S-step formulations are designed to reduce the number of global synchronizations associated with the calculation of vector inner products. These formulations may, when combined with communication-reducing methods such as additive Schwarz preconditioning, form the basis for a set of optimal Krylov solvers for many-GPU calculations.

Speaker: Dr Justin Foley (Microway and Nvidia)

Slides jfoley_talk.pdf

45 Coulomb and Landau Gauge Fixing in GPUs using CUDA and MILC

In this work, we present the GPU implementation of the overrelaxation and steepest descent method with Fourier acceleration methods for Laudau and Coulomb gauge fixing using CUDA for SU(N) with N>2. A multi-GPU implementation of the overrelaxation method is also presented using MPI and CUDA. The GPU performance was measured on BlueWaters and compared against the gauge fixing of the CPU MILC code.

Speaker: Dr Nuno Cardoso (NCSA, University of Illinois)

Slides Talk_Cardoso_Nuno.pdf

46 Staggered Dslash Performance on Intel Xeon Phi Architecture

The conjugate gradient algorithm is among the most essential and time consuming parts of lattice calculations with staggered quarks. We test the performance of dslash, the key step in the CG algorithm, on the Intel Xeon Phi, also known as the many integrated cores (MIC) architecture, with different parallelization strategies using MPI,OpenMP, and the vector processing units (VPUs).

Speaker: Ms Ruizi Li (Indiana University)

Slides MIC_presentation_4.pdf

Hadron Structure: Parallel 2D

Convener: Will Detmold

47 Decay constants of the pion and its excitations on the lattice

We present a lattice QCD calculation of the ratios of decay constants of the excited states of the pion, to that of the pion ground state. We use an anisotropic clover fermion action with three flavors of quarks, and study the pion decay constants at three values of the light-quark masses, corresponding to pion masses of 391, 524 and 702 MeV. We find that the decay constant of the first excitation, and more notably of the second, is suppressed with respect to that of the ground-state pion, but that the suppression shows little dependence on the quark mass. The strong suppression of the decay constant of the second excited state is consistent with its interpretation as a predominantly hybrid state.

Speaker: Mrs Ekaterina Mastropas (College of William and Mary)

Slides Mastropas.pdf

48 Volume effects on the method of extracting form factors at zero momentum

The Rome method allows one to extract form factors using lattice computations performed strictly at zero momentum. We investigate the size of finite volume effects resulting from this method. As a test case, we focus on the pion charge radius and show how to ascertain the finite volume effect with the aid of chiral perturbation theory. The framework developed can easily be generalized to account for modified infrared physics of other low-energy matrix elements extracted at zero momentum.

Speaker: Prof. Brian Tiburzi (City College of New York)

Slides voleff.pdf

49 Pi N Sigma Term and Scalar Form Factor from Overlap Fermion

We report our calculation of the pi N sigma term and scalar form factor from the overlap fermion on 2+1 flavor domain wall fermion configurations on the 24^3 x 64 lattice at the sea quark mass which corresponds to the pion mass at 330 MeV. The improvement of the nucleon propagator and the quark loop with low mode average will be discussed.

Speaker: Prof. Keh-Fei Liu (University of Kentucky)

Slides piNsigam.pdf

Hadron spectroscopy and interaction: Parallel 2B

Convener: Dr Marcus Petschlies (Cyprus Institute / CaSToRC)

50 Charm in Lattice QCD with Domain-Wall Fermion

We study the charm physics in two-flavors lattice QCD with optimal domain-wall fermion. The gauge ensembles are generated on the $24^3 \times 48 $ lattice with the extent in the fifth dimension $ N_s = 16 $, and the plaquette gauge action at $ \beta = 6.10 $, for three sea-quark masses corresponding to the pion masses in the range 265-465 MeV. We determine the lattice spacing by the Wilson flow, and the strange and the charm quark masses by the masses of the vector mesons $ \phi(1020) $ and $ J/\psi(3097) $ respectively. We compute the point-to-point quark propagators and measure the time-correlation functions of all 2-quark meson interpolators, and determine the lowest-lying mass spectra of charmed mesons with quark contents c-cbar, c-sbar and c-dbar. Moreover, we determine the pseudoscalar decay constants $ f_K $, $ f_D $ and $ f_{D_s} $, which are in good agreement with the experimental values.

Speaker: Prof. Ting-Wai Chiu (National Taiwan University)

Slides twchiu_140623.pdf

51 Hadron spectra and Delta_mix from overlap quarks on a HISQ sea.

We present results of our continuing study on mixed-action hadron spectra and decay constants using overlap valence quarks on MILC's 2+1+1 flavor HISQ gauge configurations. This study is carried out on three lattice spacings, with charm and strange masses tuned to their physical values, and with m_l/m_s = 1/5. I will discuss a determination of the mixed-action parameter Delta_mix, which enters into chiral formulae for the masses and decay constants.

Speaker: Dr Andrew Lytle (TIFR)

Slides dmix.pdf

52 Spectroscopy of charmed baryons from lattice QCD

We present the ground and excited state spectra of triply, doubly and singly-charmed baryons by using dynamical lattice QCD. A large set of baryonic operators that respect the symmetries of the lattice and are obtained after subduction from their continuum analogues are utilized. Using novel computational techniques correlation functions of these operators are generated and the variational method is exploited to extract excited states. The lattice spectra that we obtain have baryonic states with well-defined total spins up to $\frac{7}{2}$ and the low lying states remarkably resemble the expectations of quantum numbers from SU(6)$\times$ O(3) symmetry. Various energy splittings between the extracted states, including splittings due to hyperfine as well as spin-orbit coupling, are considered and those are also compared against similar energy splittings at other quark masses.

Speaker: Dr Padmanath Madanagopalan (Institute of Physics, University of Graz)

Slides Padmanath_Lat14.pdf

53 Low lying charmonium states at the physical point

We present results for the mass splittings of low-lying charmonium states from a calculation of Wilson clover quarks with the Fermilab interpretation on an asqtad sea. We use five lattice spacings and two values of the light sea quarks to extrapolate our results to the physical point. Sources of systematic uncertainty in our calculation are discussed and we compare our results for the 1S hyperfine splitting, the 1P-1S splitting and the P-wave spin orbit and tensor splittings to experiment.

Speaker: Dr Daniel Mohler (Fermilab)

Slides lattice2014_mohler.pdf

54 DK and D* K scattering near threshold

We study the three D_s quantum channels J^P = 0^+, 1^+ and 2^+ where experiments have identified the charm-strange states D*_s0 (2317), D_s1(2460), D_s1(2536) near the DK and D*K thresholds, and D*_s2(2573). We consider correlation functions for sets of qbar q operators and, for J^P = 0^+, 1^+, also the DK and D*K meson-meson interpolators and determine for these cases values of the elastic scattering amplitude. Constructing the full set of correlators requires propagators which connect any pair of lattice sites. For one ensemble of gauge configurations (32^3 x 64, m_pi= 156 MeV) a stochastic distillation variant is employed and for another ensemble (16^3 x 32, m_pi= 266 MeV) we use the full distillation method. Both, D*_s0(2317) and D_s1(2460), are found as bound states below threshold, whereas D_s1(2536), and D*_s2(2573) are identified as narrow resonances close to the experimental masses.

Speaker: C. B. Lang (Univ. Graz)

Slides LAT2014_c_b_lang.pdf

55 Conserved currents and results from 2+1f dynamical Mobius DWF simulations at the physical point

We discuss the construction of the almost conserved axial and exactly conserved vector currents in the Mobius generalisation of DWF at finite Ls. I then report on the status of 2+1f DWF simulations at the physical point, with a focus on the determinations of the lattice spacings, and of the pion and kaon decay constants and the Kaon bag parameter in the continuum limit.

Speaker: Dr Peter Boyle (University of Edinburgh)

Slides conserved.pdf

Nonzero temperature and Density: Parallel 2A

Convener: Ludmila Levkova

56 Fluctuations of the electric charge in theory and experiment

We present the continuum extrapolated kurtosis, skewness and variance of the electric charge in a grand canonical ensemble with zero or small chemical potential. This observable his a particular relevance in Heavy Ion Physics since ratios of such fluctuations have been measured in experiment at the chemical freeze-out. We discuss how lattice results describe the STAR fluctuation data at RHIC and show a thermometer candidate for the LHC.

Speaker: Dr Szabolcs Borsanyi (Bergische Universität Wuppertal)

Slides lattice14_charge.pdf

57 Thermodynamics of heavy-light hadrons

Ratios of cumulants of conserved net charge fluctuations are sensitive to the degrees of freedom that are carriers of the corresponding quantum numbers in different phases of strong interaction matter. We calculate second and fourth order cumulants of net charm and strange fluctuations and their correlations with other conserved charges such as net baryon number and electric charge. Simulation are performed on Nt=6,8,12 lattices using the Highly Improved Staggered Quark (HISQ) action with a light to strange quark mass ratio of 1/20 and having charm quarks treated in the quenched approximation. Analyzing appropriate ratios of these cumulants we observe that both open strange and charm hadrons start to get deconfined in the chiral crossover region. We provide evidence for additional, experimentally yet unobserved open charm and strange hadrons from QCD thermodynamics by comparing lattice QCD results to Hadron Resonance Gas model calculations performed with a hadron spectrum as listed in the Particle Data Tables as well as with a spectrum predicted in relativistic quark model and observed in lattice QCD calculations. We also discuss the influence of these yet unobserved states on the determination of freeze-out temperature and chemical potentials from heavy ion collision experiments.

Speaker: Prof. Heng-Tong DING (Central China Normal University)

Slides HengTong_lattice14.pdf

58 Exploring the QCD phase diagram with conserved charge fluctutaions

Higher order cumulants of fluctuations of conserved charges are an important diagnostic tool for the thermodynamic properties of strong interacting matter close to freeze out at LHC energies as well as in the entire energy range covered with the beam energy scan (BES) at RHIC. We present recent progress on the calculation of conserved charge fluctuations with highly improved staggered quarks (HISQ action). In particular we will focus on higher order cumulants up to the 6th order of net baryon number, net electric charge and net strangeness fluctuations. We will discuss how these quantities approach the hadron resonance gas at low temperatures and to what extent they show sensitivity to universal scaling behavior. Based on this analysis we discuss possible consequences for the QCD phase diagram and the radius of convergence of the Taylor expansion of the QCD partition function. The latter can be used to locate the QCD critical point. Furthermore, we specify a procedure to extract freeze-out conditions from various ratios of conserved charge fluctuations measured in the BES at RHIC.

Speaker: Dr Christian Schmidt (Universitaet Bielefeld)

Slides Schmidt_latt14.pdf

59 Fluctuation effects on QCD phase diagram at strong coupling

We investigate QCD phase diagram at strong coupling based on strong coupling expansion in auxiliary field Monte-Carlo (AFMC) method. The strong coupling expansion is one of the ways to reduce the sign problem since the effective action is described in hadronic degrees of freedom via analytic integration over link variables. We have found that hadron phase is compressed (extended) at low (high) chemical potential [1] as shown in monomer-dimer-polymer simulation [2] in the strong coupling limit (SCL). We need to consider finite coupling effects to know the influence on phase diagram and the sign problem. The AFMC is a natural extension to the mean field method, which let us include finite coupling and fluctuation effects straightforwardly. In the presentation, we will give some results on QCD phase diagram in SCL. We will also discuss next-to-leading order effects in the strong coupling expansion. [1] T. Ichihara, A. Ohnishi, T. Z. Nakano, arXiv:1401.4647 [hep-lat]. [2] W. Unger, P. de Forcrand, J. Phys. G38 (2011) 124190.

Speaker: Mr Terukazu Ichihara (Yukawa Institute for Theoretical Physics and Kyoto University)

Slides Lattice14-0622.pdf

60 On curing the divergences in the quark number susceptibility

Quark number susceptibility on the lattice, obtained by merely adding a \mu N-term with \mu as the chemical potential and N as the conserved quark number, has a quadratic divergence in the cut-off a. We show that it is simply a faithful representation of the corresponding continuum result. While one can eliminate it in the free theory by suitably modifying the action, as is popularly done, it can simply be subtracted off as well. Computations of higher order susceptibilities, needed for estimating the location of the QCD critical point, then need a lot fewer number of quark propagators are at any order. We show that in the interacting theory this method of divergence removal works.

Speaker: Prof. Rajiv Gavai (Tata Institute of Fundamental Research)

Slides Gavai0623.pdf

61 The Combinatorics of Lattice QCD at Strong Coupling

We compare the combinatorics of staggered and Wilson fermions in the strong coupling limit for various colors and flavors. Based on the hopping parameter expansion, we express the partition functions of both discretizations in terms of polynomials with coefficients of distinct combinatorical interpretation. We address how gauge corrections to the strong coupling limit modify the combinatorics and possibly make both lattice discretizations more similar in the continuum limit. We compare our analytic results by some recent numerical findings obtained at finite temperature and density.

Speaker: Dr Wolfgang Unger (University Frankfurt)

Slides UngerLat14.pdf

Nonzero temperature and Density: Parallel 2E

Convener: Ion-Olimpiu Stamatescu

62 Deconfinement transition as a black hole formation by the condensation of QCD string

In the gauge/gravity duality, the deconfinement transition in the gauge theory is identified with a formation of black hole in the dual gravity theory. In this talk, firstly we give quantitative evidence for this identification from the thermodynamic study of the supersymmetric theory. Then we consider generic gauge theories, including QCD, and show that the deconfinement transition is the condensation of very long and self-intersecting QCD strings, which is analogous to the formation of a black hole in string theory. We provide a concrete picture by using lattice gauge theory and matrix models in the Hamiltonian formulation, and give numerical evidence supporting this interpretation. As a by-product we derive an analytic formula for the deconfinement temperature of the lattice gauge theory in the strong coupling limit. We also argue how the fast thermalization of the QGP can be understood from this viewpoint. This talk is based on the following work: Hanada, Hyakutake, Ishiki and Nishimura, Science (2014)[arxiv:1311.5607]. Hanada, Maltz and Susskind, arxiv:1405.****[hep-th], to appear. Berkowitz, Hanada, Hayden and Susskind, in progress.

Speaker: Masanori Hanada (Stanford/Kyoto)

Slides LATTICE2014_hanada.pdf

63 Gluonic Correlations at Deconfinement

We investigate the critical behavior of electric and magnetic gluon propagators around the deconfinement temperature of SU(2) gauge theory on large lattices, employing Landau gauge. In particular, we study the analytic properties of these propagators using several trial fitting functions.

Speaker: Tereza Mendes (University of Sao Paulo)

Slides mendes_lat14.pdf

64 Locating the critical end-point of QCD

I will give an overview on our recent results for the phase diagram of QCD with Nf=2+1 and Nf=2+1+1 flavors. We use a combination of lattice and Dyson-Schwinger methods to determine the chiral and deconfinement order parameters at finite temperature and chemical potential. We find a critical end-point at large chemical potential in the vicinity of the chiral critical line extrapolated from lattice QCD.

Speaker: Prof. Christian Fischer (JLU Giessen)

Slides Lattice14_Fischer.pdf

65 Quark number density at imaginary chemical potential and its extrapolation to large real chemical potential by the effective model

We evaluate quark number densities at imaginary chemical potential by doing lattice QCD calculations on an 8^2*16*4 lattice with clover-improved Wilson quarks of two flavors. The quark number densities are extrapolated to the small real chemical potential region by assuming some function forms. The extrapolated quark number densities are consistent with those calculated at real chemical potential directly with the Taylor expansion method for the reweighing factors. Further extrapolation is also made to the large real chemical potential with the two-phase model consisting of the Walecka model for the hadron phase and the entanglement-PNJL model for the quark phase. The Walecka model is constructed to reproduce nuclear saturation properties, while the entanglement-PNJL model well account for temperature dependence of two-flavor lattice data for the order parameters such as the Polyakov loop, the thermodynamic quantities and the screening masses. Finally, we explore the hadron-quark phase transition with the two-phase model in the entire region of QCD phase diagram and discuss whether the phase diagram is consistent with two-solar mass observation of neutron stars.

Speaker: Mr Junichi Takahashi (Kyushu University)

Slides lattice2014_takahashi.pdf

66 Temperature dependence of meson screening masses; a comparison of effective model with lattice QCD

We analyze the pion screening mass calculated with lattice QCD, using the entanglement-PNJL (EPNJL) model. The EPNJL model well reproduces the lattice QCD result. We then predict the sigma meson screening mass with the model. The chiral symmetry restoration can be exhibited by the difference between the pi and sigma meson screening masses. After the chiral symmetry restoration, the two screening masses rapidly approach the free-field limit from below. Furthermore, we consider the effective restoration of the axial symmetry from lattice QCD results on a0 and pi meson screening masses. Finally, we investigate the order of the two- flavor chiral phase transition in the chiral limit.

Speaker: Mr Masahiro Ishii (Kyushu University)

Slides Ishii.pdf

67 Renormalization group flow of linear sigma model with UA(1) anomaly

Motivated by recent arguments on effective restoration of UA(1) symmetry around the critical temperature in two-flavor QCD, we investigate the renormalization group flow of the U(2)xU(2) linear sigma model (LSM) with the traditional epsilon expansion. Introducing the UA(1) violation, the attractive basin falling into the O(4) LSM in the parameter space and its dependence on the size of UA(1) violation are determined. Employing a mass-dependent renormalization scheme, we also look into how the theory with 8 degrees of freedom (U(2)xU(2) LSM) reduces the one with 4 (O(4) LSM).

Speaker: Mr Tomomi Sato (The Graduate University for Advanced Studies)

Slides T_Sato(LATTICE2014).pdf

Physics beyond the standard model: 2C

Convener: Luigi Del Debbio

68 Higgs physics near the conformal window

We will use the minimal composite Higgs model to discuss theoretically and phenomenologically important issues imposed on the low mass near-conformal composite scalar of BSM Higgs physics.

Speaker: Dr Julius Kuti (U.C. San Diego)

Slides jkLattice2014v2.pdf

69 The low mass scalar impostor and the composite Higgs

The widely discussed near-conformal gauge theory with two fermion flavors in the two index symmetric (sextet) representation of the SU(3) color gauge group is the minimal realization of the composite Higgs mechanism. A comprehensive study of flavor singlet scalar spectroscopy with Higgs quantum numbers is reported based on extended new data sets.

Speaker: Mr chik him wong (University of California, San Diego)

Slides presentation.pdf

70 Testing composite Higgs models on the lattice

Composite Higgs dynamics due to a new gauge sector has recently attracted renewed interest both phenomenologically and on the lattice. In fact, while a scalar particle consistent with the Standard Model Higgs has been discovered at the LHC, the detailed nature of this particle remains unknown. One popular description is that the Higgs is a result of a strongly coupled composite framework, such as models based on the SU(4)/Sp(4) coset. One fundamental theory that yields this coset is an SU(2) gauge theory with 2 flavors in the fundamental representation. We study the spectrum of this theory on the lattice and look at the flavor-singlet scalar channel, where the Higgs particle could emerge as an excitation of the fermion condensate.

Speaker: Dr Enrico Rinaldi (Physics Division, Lawrence Livermore National Laboratory)

Slides Rinaldi_E_Lattice2014_2C_FINAL.pdf

71 Targeting the Conformal Window: Measuring the 0++ Scalar

The light Higgs boson of the Standard Model could arise as the consequence of the weakly broken conformal symmetry in a strongly interacting gauge theory just below the conformal window. Here we present a novel idea to study the transition from conformal to confining behavior using an SU(3) gauge theory with four light and eight heavy flavors. This system interpolates between the 12 flavor conformal and the 4 flavor chirally broken theory as the mass of the heavy flavors are varied. We show first results on the determination of the isosinglet 0++ state as it interpolates between QCD-like and conformal behavior.

Speaker: Mr Evan Weinberg (Boston University)

Slides weinberg_evan_lattice2014.pdf

72 Gauge and Higgs boson masses from an extra dimension

We present novel calculations of the mass hierarchy of the $SU(2)$ pure gauge theory on a space-time lattice with an orbifolded fifth dimension. This theory has three parameters; the gauge coupling $\beta$, the anisotropy $\gamma$, which is a measure of the ratio of the lattice spacing in the four dimensions to that in the fifth dimension, and the extent of the extra dimension $N_{5}$. Using a large basis of scalar and vector operators we explore in detail the spectrum along the $\gamma = 1$ line, and for the first time we investigate the dependence of the spectrum on $N_{5}$ and $\gamma$.

Speaker: Dr Graham Moir (University of WUppertal)

Slides lattice_talk_2014.pdf

73 Composite (Goldstone) Higgs Dynamics on the Lattice: Spectrum of SU(2) Gauge Theory with two Fundamental Fermions

We study the meson spectrum of SU(2) gauge theory with two Wilson fermions in the fundamental representation. The theory unifies both Technicolor and composite pseudo Goldstone Boson (pGB) Higgs models of electroweak symmetry breaking. We have calculated the masses of the lightest spin one vector and axial vector mesons. In addition, we have also obtained preliminary results for the mass of the lightest scalar (singlet) meson state. The simulations have been done with multiple masses and two different lattice spacings for chiral and continuum extrapolations. The spin one meson masses set lower limits for accelerator experiments, whereas the scalar meson will mix with a pGB of the theory and produce two scalar states. The lighter of the states is the 125 GeV Higgs boson, and the heavier would be a new yet unobserved scalar state.

Speaker: Dr Ari Hietanen (CP3-Origins, SDU)

Slides su2.pdf

Weak Decays and Matrix Elements: Parallel 2G

Convener: Dr Andreas Juettner (University of Southampton)

74 Calculation of $K \to \pi\pi$ decay amplitudes with improved Wilson fermion in 2+1 flavor lattice QCD

We presnet our results of the $K\to\pi\pi$ decay amplitudes for both the $\Delta I=1/2$ and $3/2$ channels. Calculations are carried out with $N_f=2+1$ gauge configurations previously generated by the PACS-CS Collaboration with the Iwasaki gauge action and nonperturbatively $O(a)$-improved Wilson fermion at $a=0.091\,{\rm fm}$ and $m_\pi=280\,{\rm MeV}$ on a $32^3\times 64$ ($La=2.9 {\rm fm}$) lattice. For the calculation of quark loop at the weak operator in the disconnected diagram, we use the stochastic method with the hopping parameter expansion technique and the truncated solver method proposed by Bali et al.. We find that these are very efficient methods.

Speaker: Dr Naruhito Ishizuka (University of Tsukuba)

Slides lat14_tp.pdf

75 Lattice Measurement of the Delta I=1/2 Contribution to Standard Model Direct CP-Violation in K->pi pi Decays at Physical Kinematics: Part I

The RBC & UKQCD collaborations have recently published lattice results for the K->pi pi decay amplitude in the I=2 channel, A_2, and improved results will be presented at this conference. In this presentation we discuss the determination of the I=0 channel amplitude, A_0. Combining this with A_2 provides epsilon', the measure of direct CP-violation in the Standard Model. In part I we provide an overview of the project and detail our use of G-parity boundary conditions to achieve physical kinematics in the decay, as well as discussing the ongoing generation of the specialized lattices required.

Speaker: Dr Christopher Kelly (Brookhaven National Laboratory)

Slides talk_v2.pdf

76 Lattice Measurement of the Delta I=1/2 Contribution to Standard Model Direct CP-Violation in K->pi pi Decays at Physical Kinematics: Part II

In continuation of part I, I will discuss our use of all-to-all propagators in order to construct pi-pi operators with reduced coupling to the vacuum, which helps to reduce the noise in the K->pipi(I=0) decay amplitude. I will also present preliminary results for the pipi(I=0) phase shift, decay amplitude A_0, both with physical kinematics. The precise value of A_0, once computed, will provide the measure of direct CP-violation epsilon prime, on the lattice.

Speaker: Mr Daiqian Zhang (Columbia University)

Slides DaiqianZhang2014

77 Rare kaon decays from lattice QCD

The rare kaon decays, $K \to pi nu nu_bar$ and $K \to pi l^+ l^-$, serve as ideal probes for the observation of New Physics (NP) effects. To isolate the NP contributions successfully, one needs to control the errors for Standard Model prediction from both short- and long-distance contributions. RBC-UKQCD collaborations have performed a successful exploratory study on the calculation of the long-distance contributions to KL-KS mass difference, and are now developing the necessary methods to calculate the long-distance contributions to rare kaon decay amplitudes. In this talk, I will introduce the physical background for rare kaon decays and describe the state of our preliminary calculations.

Speaker: Dr Xu Feng (Columbia University)

Slides rare_kaon.pdf

78 Kl - Ks mass difference computed with a 171 MeV pion mass

In this work, I used a $32^3 \times 64 \times 32$, 2+1 flavor domain wall lattice with Iwasaki+DSDR gauge action. The pion mass is 171 MeV and the kaon mass is 492 MeV. We implement the Glashow-Iliopoulos-Maiani (GIM) cancellation using charm quark masses of 750 MeV and 592 MeV. This is an intermediate calculation, in that we are using both a coarse lattice spacing (1/a = 1.37GeV) so we expect significant discretization error coming from charm quark mass and we are also using unphysical kinematics for the pion. The main purpose of this calculation is to identify the contribution from the two pion intermediate state when the energy of a two pion state is smaller than that of the kaon.

Speaker: Mr Ziyuan Bai (Columbia University in the city of New York)

Slides slides.pdf

79 The Kaon Semileptonic Form Factor from Domain Wall QCD at the Physical Point

We present an update on the RBC/UKQCD collaboration’s calculation of the kaon semileptonic form factor at zero momentum transfer, $f_{+}^{K \pi}(0)$. This calculation utilizes two new $N_{f} = 2+1$ M\"{o}bius Domain Wall Fermion ensembles which allow us to simulate QCD directly at physical pion mass for the first time. Together with our previous results we now have a complete set of measurements extending from the $SU(3)$ symmetric limit down to the physical point, allowing us to minimize systematic error associated with the chiral extrapolation.

Speaker: Mr David Murphy (Columbia University)

Slides Murphy.pdf

Tuesday, 24 June

Plenary

Convener: Dr Akira Ukawa (Riken AICS)

80 K/pi physics

Speaker: Prof. Nicolas Garron (Trinity College Dublin)

Slides kaon_pion.pdf

81 Validity of ChPT -- is M_\pi=135MeV small enough ?

Speaker: Dr Stephan Durr (Wuppertal University / Juelich Forschungszentrum)

Slides lat14_talk.pdf

82 Multigrid for Lattice QCD

Speaker: Prof. Andreas Frommer (University of Wuppertal)

Slides talk_frommer.pdf

10:45 Coffee Break

Plenary

Convener: Dr Robert Edwards (Jefferson Lab)

83 Few-body physics

Few-body hadronic observables play an essential role in a wide number of processes relevant for both particle and nuclear physics. In order for Lattice QCD to offer insight into the interpretation of few-body states, a theoretical infrastructure must be developed to map Euclidean-time correlation functions to the desired Minkowski-time few-body observables. In this talk, I will first review the formal challenges associated with the studies of such systems via Lattice QCD, as first introduced by Maiani and Testa, and then review methodology to circumvent said limitations. The first main example of the latter is the formalism of Luscher to analyze elastic scattering and a second is the method of Lellouch & Luscher to analyze weak decays. I will then proceed to discus recent theoretical generalizations of these frameworks that allow for the determination of scattering amplitudes, resonances, transition and elastic form factors. Finally, I will outline outstanding problems, including those that are now beginning to be addressed.

Speaker: Dr Raul Briceno (JLab)

Slides lattice_2014.pdf

84 Hadronic Interaction

Speaker: Dr Takeshi Yamazaki (KMI-Nagoya)

Slides lattice.pdf

Hadron Structure: Parallel 3D

Convener: Kostas Orginos

85 Initial nucleon structure results with chiral quarks at the physical point

I will report initial nucleon structure results computed on lattices with 2+1 dynamical Moebius domain wall fermions at the physical point generated by RBC and UKQCD. At this stage, we evaluate only connected quark contributions. In particular, I will discuss the nucleon electric and magnetic radii, quark contributions to the nucleon spin, the nucleon axial charge, and the quark momentum fraction. From the currently available statistics, we estimate that within a year our stochastic + excited states-systematic errors for the nucleon electric radius will approach the level of the discrepancy between the two experimental values. To reduce the computational cost of our calculations, we extensively use acceleration techniques such as low-eigenmode deflation and all-mode-averaging.

Speaker: Dr Sergey Syritsyn (RIKEN-BNL Research Center)

Slides syritsyn-lattice2014.pdf

86 News from hadron structure calculations with twisted mass fermions

We report on the ongoing calculations of the European Twisten Mass Collaboration concerning the non-perturbative study of hadron structure. We discuss the status of these computations at the examples of various moments of parton distribution functions and give an update about the calculations for x_g and the full quark PDF of the nucleon.

Speaker: Mr Christian Wiese (DESY, Zeuthen)

Slides wiese_lattice.pdf

87 Nucleon and pion structure in n_f=2 QCD

We determine singlet and non-singlet hadron structure matrix elements for the nucleon and the pion from n_f=2 simulations at the physical quark mass.

Speaker: Prof. Gunnar Bali (University of Regensburg)

Slides talk.pdf

88 Hadron mass decomposition from Lattice QCD

Based on the lattice simulation with overlap fermions on 2+1 DWF fermion configurations on the 24^3 x 64 lattice, we carry out the first lattice QCD calculation of the quark and glue contributions to pseudoscalar and vector mesons and the nucleon. The quark mass term contributes about 50% to the mass of the light pseudoscalar mesons; whereas, it is not important in the masses of light vector mesons and the nucleon. With the QCD Hamiltonian and the trace anomaly, the glue components are deduced. They play an important role in the mass of the light hadrons.

Speaker: Dr yibo yang (University of Kentucky)

Slides mass_decomp.pdf

89 Quark Spin in the Nucleon with Overlap Fermion

The disconnected insertion part of the quark contributions to the nucleon spin are calculated with overlap fermion on DWF configurations. This work is done by calculating the disconnected three point correlation functions through the anomalous Ward identity. The quark loop of the pseudoscalar density is calculated with low-mode average and grid-noise estimate for the high modes. The overlap operator is used for the topological charge density.

Speaker: Dr Ming Gong (Institute of High Energy Physics, Chinese Academy of Sciences)

Slides Gongming_lattice2014.pdf

Hadron spectroscopy and interaction: Parallel 3B

Convener: Prof. Shailesh Chandrasekharan (Duke University)

90 Relativistic three-particle quantization condition: an update

Last year, we presented a generalization of Luescher's two-particle quantization condition to three identical, degenerate particles. While completing this work, we discovered a technical problem with our derivation which invalidated the result, in the sense that not all finite-volume corrections that fall as powers of the box size were controlled. We have found a fix to this problem, which maintains the form of our original result, but involves a new infinite-volume quantity that is not directly related to the three-particle scattering amplitude. We will sketch the problem and its resolution, and discuss the practical utility of our result.

Speaker: Prof. Stephen Sharpe (University of Washington)

Slides sharpe_lat14.pdf

91 On the extraction of spectral quantities with open boundary conditions.

We discuss methods to extract decay constants, meson masses and gluonic observables in the presence of open boundary conditions. Our CLS ensembles have 2+1 flavours of O(a)-improved Wilson fermions and are generated with a small twisted mass as proposed by Luescher and Palombi. We analyse the associated reweighting for different observables.

Speaker: Mr Mattia Bruno (DESY, Zeuthen)

Slides bruno_lat14.pdf

92 Gradient Flow Analysis on MILC HISQ Ensembles

We present a final analysis of gradient flow and the associated scale $w_0$ measured on the $N_f=2+1+1$ HISQ ensembles. Compared to previously reported results, we have improved the interpolation to physical quark masses using chiral perturbation theory, adjusted for variations in charm quark mass between ensembles, and derived a `prediction' function for estimating the scale using $w_0/a$ on new ensembles with unphysical quark masses. Additional results include a comparison of $t_0/a$ to $w_0/a$ and a test of agreement between the RHMC and RHMD generation algorithms.

Speaker: Nathan Brown (Washington University in St. Louis)

Slides finalGF_LAT14_NBrown.pdf

93 Simulating two dimensional two-color QCD using purely bosonic variables

The numerical calculation of the fermion determinant is one of the most costly computational tasks in lattice QCD. For massless two-color QCD in two dimensions we are able to calculate the fermion determinant analytically, allowing us to obtain high precision results for the mass spectrum of the theory. In the talk we review our lattice formulation in terms of purely bosonic variables and present first results on the mass spectrum.

Speaker: Mr Daniel August (friedrich schiller universität jena)

Slides augustlattice2014.pdf

94 Radial and orbital excitation energies of charmonium

The system of charmonium has several excited states below the energy threshold for decay into D and Dbar mesons, which can in principle be studied accurately in lattice QCD. Studies that include many states in the spectrum have typically only been done at one value of the lattice spacing and with light quarks in the sea. Here we give results for radial and orbital excitation energies for charmonium from a calculation on 2+1+1 MILC configurations at multiple lattice spacings and including physical values for u/d quark masses. We use the HISQ formulation for c for small discretisation errors and smeared operators to improve excited state overlap.

Speaker: Mr Ben Galloway (University of Glasgow)

Slides Galloway_Lattice2014.pdf

Nonzero temperature and Density: Parallel 3A

Convener: Rajiv Gavai

95 The N_f=3 critical endpoint with smeared staggered quarks

We present preliminary results for the determination of the critical endpoint of the chiral transition in N_f=3 QCD with mu=0 at small N_t. We have employed an unimproved Wilson gauge action with staggered fermions, for which previous results on the critical endpoint are available. As an extension of these results we have studied the dependence of the critical mass on the strength of the smearing.

Speaker: Mr Lukas Varnhorst (Bergische Universität Wuppertal)

Slides varnhorst.pdf

96 Update on the critical endpoint of the finite temperature phase transition for three flavor QCD with clover type fermions

We present preliminary results on the critical endpoint of three flavor QCD at zero chemical potential. We employ the renormalization-group improved Iwasaki gauge action and $O(a)$-improved Wilson fermion action. The critical endpoint is determined by using the intersection points of kurtosis for mixed observable as well as plaquette, gange action density, Polyakov loop and "chiral condensate" at the temporal size $N_t$=4, 6 and 8.

Speaker: Dr Yoshifumi Nakamura (RIKEN Advanced Institute for Computational Science)

Slides lat14.pdf

97 Scalar correlators near the 3-flavor thermal critical point

We investigate screening masses at finite temperatures with 3 flavors using the non-perturbatively improved clover fermion action and the Iwasaki gauge action. This report focuses on the behavior of the scalar singlet correlator near the thermal critical point. I will explain the technique used to extract the correlator and discuss our preliminary results from ensembles at Nt=8.

Speaker: Xiao-Yong Jin (RIKEN Advanced Institute for Computational Science)

Slides jin_Talk_lattice2014_v1.pdf

98 Critical end point in Nf=3 QCD with finite density and temperature

We investigate a presence of critical end point in finite density/temperature QCD with three-degenerated Wilson-Clover quarks. The critical end point is estimated by the kurtosis intersection method and a gap of transition points between two independent observables. We also discuss slope/curvature of the critical end line extending from the zero density point whose details will be given in a talk by Y.Nakamura.

Speaker: Dr Shinji TAKEDA (Kanazawa University)

Slides takeda_lat2014_20140624.pdf

99 Search for the chiral phase transition in three flavor QCD at imaginary chemical potential

The finite temperature transition of QCD with three degenerate flavors is expected to become a first order phase transition at small quark masses. It has been observed that introducing a sufficiently large imaginary chemical potential broadens the first order region and raises the critical quark mass to the numerically feasible regime. We report on our search for this first order transition at imaginary chemical potentials using three flavors of staggered quarks.

Speaker: Dr Balint Toth (University of Wuppertal)

Slides tothb_l2014.pdf

Physics beyond the standard model: Parallel 3C

Convener: David Lin

100 Beyond the Standard Model Kaon Mixing from Mixed-Action Lattice Simulations

We calculate matrix elements for beyond-the-Standard-Model contributions to neutral kaon mixing from mixed-action lattice simulations with staggered sea quarks and domain-wall valence quarks. We analyze the (2+1)-flavor MILC asqtad ensembles with multiple light sea-quark masses corresponding to staggered pions as light as 220 MeV on three different lattice spacings a ~ 0.12, 0.09, and 0.06 fm, and extrapolate our data to the physical light-quark masses and continuum using mixed-action chiral perturbation theory. We renormalize the matrix elements using mean-field improved lattice perturbation theory at one loop to obtain continuum values in the MS-bar scheme. Once our analysis is finalized, our results will help to improve constraints on new physics from experimental measurements of neutral kaon mixing.

Speaker: Mr Maxwell Hansen (University of Washington)

Slides Hansen_Lattice2014.pdf

101 Beyond the Standard Model Matrix Elements with the gradient flow

With the gradient flow, we propose to calculate the QCD component of key beyond the Standard Model (BSM) matrix elements related to quark and strong theta-CP violations and the strange scalar content within the nucleon. The former set of matrix elements impacts our understanding of Electric Dipole Moments (EDMs) of nucleons and nuclei (a key signature of BSM physics), while the latter contributes to elastic recoil of Dark Matter particles of nucleons and nuclei. If successful, these results will lay the foundation for extraction of BSM observables from future low-energy, high-intensity and high-accuracy experimental measurements.

Speaker: Dr Andrea Shindler (Forschungszentrum Jülich)

Standard model parameters and renormalization: Parallel 3G

Convener: Dr Georg von Hippel (University of Mainz)

102 A perturbative study of the chirally rotated Schrödinger functional in QCD

The chirally rotated Schrödinger functional renders the mechanism of automatic O(a) improvement compatible with the Schrödinger functional (SF) formulation. We here report on the determination to 1-loop order in perturbation theory of the renormalization coefficients necessary to achieve automatic O(a) improvement and the boundary improvement coefficients needed to eliminate the extra boundary O(a) effects present in any SF formulation. After this is done, we perform a set of tests of automatic O(a) improvement and of the universality between standard and chirally rotated SF formulations. Finally we discuss the determination of the non-singlet current renormalization constants ZA and ZV from ratios of 2-point functions in the chirally rotated setup.

Speaker: Dr Pol Vilaseca Mainar (Instituto Nazionale di FIsica Nucleare)

Slides pol_vilaseca_lat2014.pdf

103 A dynamical study of the chirally rotated Schrödinger functional in QCD

The chirally rotated Schrödinger functional for Wilson quarks allows for finite-volume, mass-independent renormalization schemes compatible with automatic O(a)-improvement. So far, in QCD, the setup has only been studied in the quenched approximation. Here we present first results for Nf=2 dynamical flavors for several renormalization factors of quark bilinears. We discuss how such renormalization factors can be easily obtained from simple ratios of two-point functions, and show how automatic O(a)-improvement is at work. We then compare our results with previous Schrödinger functional determinations.

Speaker: Mr Mattia Dalla Brida (Trinity College Dublin)

Slides lat14.pdf

104 Non perturbative renormalization and running of Delta F=2 four-fermion operators in the SF scheme.

We present preliminary results of a non-perturbative study of the scale-dependent renormalization constants of a complete basis of Delta F=2 parity-odd four-fermion operators that enter the computation of hadronic B-parameters within the SM and beyond. We consider non-perturbatively O(a) improved Wilson fermions and our gauge configurations contain two flavors of massless sea quarks. The mixing pattern of these operators is the same as for a regularization that preserves chiral symmetry, in particular there is a "physical" mixing between some of the operators. The renormalization group running matrix is computed in the continuum limit for a family of Schrödinger Functional (SF) schemes through finite volume recursive techniques. We compute non-perturbatively the relation between the renormalization group invariant operators and their counterparts renormalized in the SF at a low energy scale and we provide non-perturbative estimates for the matching matrix between the lattice regularized theory and the various SF schemes.

Speaker: Dr Mauro Papinutto (Universita "La Sapienza" and INFN Sez. di Roma)

Slides 3_NY_papinutto.pdf

105 Non-perturbative improvement of the axial current in N_f=3 lattice QCD

We present the results of a non-perturbative determination of the improvement coefficient c_A of the axial vector current in three-flavour lattice QCD with O(a) improved Wilson quarks and tree-level Symanzik improved gauge action. Our computation involves an improvement condition which is imposed at a constant physical volume of about 1.2 fm and employs the PCAC relation in the Schrödinger functional scheme with two different pseudoscalar states.

Speaker: Dr Jochen Heitger (University of Muenster)

Slides lat14sl.pdf

106 Non-perturbative renormalization of the axial current in N_f=3 lattice QCD

We report on a non-perturbative computation of the renormalization factor Z_A of the axial vector current in three-flavour O(a) improved lattice QCD with Wilson quarks and tree-level Symanzik improved gauge action. Our normalization condition is formulated at constant physics in the same Schrödinger functional setup as is being used for the determination of the improvement coefficient c_A. It exploits the full, massive axial Ward identity to reduce finite quark mass effects in the evaluation of Z_A and correlators with boundary wave functions to suppress excited state contributions in the pseudoscalar channel.

Speaker: Mr Christian Wittemeier (Westfälische Wilhelms-Universität Münster)

Slides wittemeier.pdf

Theoretical Developments: Parallel 3E

Convener: Michael G Endres (MIT)

107 Polyakov Loop Correlations at Large N

The topic of the presentation is the two-point single-eigenvalue distribution correlation function of Polyakov loops in the confined phase of four dimensional SU(N) YM theory at large N.

Speaker: Prof. Herbert Neuberger (Rutgers)

Slides lat14.pdf

108 TEK twisted gradient flow running coupling

We measure the running of the twisted gradient flow coupling in the Twisted Eguchi-Kawai (TEK) model, the SU(N) gauge theory on a single site lattice with twisted boundary conditions in the large N limit.

Speaker: Liam Keegan (CERN)

Slides talk.pdf

109 Testing volume independence of large N gauge theories on the lattice

We present the results of our direct precision test of volume independence for SU(N) Yang-Mills theory on the lattice with Wilson action. Wilson loop expectation values at large N are obtained by extrapolation and its finite volume dependence examined for different boundary conditions.

Speaker: Prof. Antonio Gonzalez-Arroyo (Instituto de Fisica Teorica UAM/CSIC)

Slides talk_lattice.pdf

110 Temperature dependence of the chiral condensate in the Schwinger model with Matrix Product States

Tensor network methods form a family of efficient techniques of approximating quantum states. Their successes in quantum many-body physics have inspired their use for lattice gauge theories. We employed one of the tensor network techniques, called Matrix Product States, to investigate the Schwinger model in the Hamiltonian formulation. In this talk, we show our results for the temperature dependence of the chiral condensate in the massless model and we compare to the analytical formula derived by Sachs and Wipf.

Speaker: Dr Hana Saito (DESY Zeuthen)

Slides Lattice2014_saitouh.pdf

111 Grassmann Tensor Renormalization Group Study of Lattice QED with Theta Term in Two Dimensions

The tensor renormalization group is one of the successful methods to tackle systems whose action is complex, though the practical calculations in higher dimensions is beyond the reach of current computer facilities. The Grassmann tensor renormalization group is a generalization to systems including fermions. As a pilot study toward lattice QCD, we apply it to two-dimensional lattice QED and investigate its phase structure with the theta term.

Speaker: Dr Yuya Shimizu (RIKEN)

Slides shimizu.pdf

Vacuum Structure and Confinement: Parallel 3F

Convener: Dr Jeff Greensite (San Francisco State University)

112 Confinement, the Abelian Decomposition, and the Contribution of Topology to the Static Quark Potential

In the past few years, we have presented a new way of considering quark confinement. Through a careful choice of a Cho-Duan-Ge Abelian Decomposition, we can construct the QCD Wilson Loop in terms of an Abelian restricted field. The relationship between the QCD and restricted string tensions is exact; and we do not need to gauge fix, apply any path ordering of gauge links, or additional path integrals. This hints at why mesons are colour neutral. Furthermore, the Abelian restricted field contains two parts: a Maxwell term, and a topological term. The topological term can describe magnetic monopoles and other topological objects, which can be studied both numerically and theoretically. By examining the topological part of the restricted field strength we have found evidence suggesting that these objects, which will contribute to confinement if present, are indeed there. Previous studies have used simplifications, breaking the exact relationship between the restricted and QCD string tensions, but it was found that the topological term dominated the restricted string tension. Here we remove those simplifications, and show that the Abelian restricted field does indeed fully explain confinement. However, we find that the topological component of the restricted field only accounts for $\sim \frac{1}{3}$ of the static quark potential, meaning that the Maxwell term also has a large contribution to the string tension. We comment on this discrepancy.

Speaker: Dr Nigel Cundy (Seoul National University)

Slides talkCundy.pdf

113 Deconfinement, Chiral Symmetry Breaking and Chiral Polarization

We examine the feasibility of the proposition that in Nf=0 QCD there is a temperature range (T_c < T < T_ch) where real Polyakov line (deconfined) vacuum exhibits valence spontaneous chiral symetry breaking and dynamical chiral polarization of Dirac eigenmodes.

Speaker: Prof. Ivan Horvath (University of Kentucky)

Slides talk_lat2014_1.pdf

114 Instanton-dyons induce both the chiral symmetry breaking and confinement

QCD topology -- mostly instantons -- had been used in the past to explain near-zero Dirac states and chiral symmetry breaking. At $T \sim T_c$ instanton are known to get decomposed into $N_c$ instanton-dyons. Several lattice observation were naturally explained by instanton-dyons. Their partition function is now numerically generated: the statistical ensemble is then used to get spectrum of Dirac eigenstates: that is found to produce both chiral broken and restored (gapped) spectra, as a function of $T$ and $N_f$. Another development is account for the back reaction, from dyons to holonomy potential. Somewhat unexpectedly, that was recently shown to induce a (quasi) confining phase transition, in which the Polyakov line jumps to zero value.

Speaker: Prof. Edward Shuryak (Stony Brook)

Slides shuryak_lattice14.pdf

115 Partial restoration of chiral symmetry inside hadrons

The presence of color source may modify the chiral condensate that characterizes the spontaneous breaking of chiral symmetry in the QCD vacuum. Using the overlap-Dirac eigenmodes, we investigate this phenomenon around static color sources representing quark-antiquark and three-quark systems. We show that the chiral condensate is reduced inside the flux-tube that is formed between the color sources. Using the three-quark system in a finite box, we estimate the magnitude of partial chiral restoration at finite density.

Speaker: Dr Takumi Iritani (High Energy Accelerator Research Organization (KEK))

Slides lattice2014_iritani.pdf

15:55 Coffee Break

Hadron Structure: Parallel 4D

Convener: Keh-Fei Liu

116 Calculation of disconnected contributions to nucleon form factors using hierarchical probing

We present results for the disconnected contributions to light-quark nucleon form factors and generalized form factors at a pion mass of approximately 300 MeV. The calculations are performed with clover fermions in a large volume, and the disconnected quark loops are evaluated using the hierarchical probing method. We compare the behavior of hierarchical probing with the traditional noise method for a wide range of observables. A large reduction of variance is observed for the electromagnetic form factors. For these form factors, we are able to clearly resolve nonzero disconnected light-quark contributions for the first time. We find that the ratio of disconnected to connected contributions to the proton electromagnetic form factors is of order 0.5%.

Speaker: Dr Stefan Meinel (Massachusetts Institute of Technology)

Slides Lattice2014_Meinel.pdf

117 Results on the disconnected contributions for hadron structure

We present results for $N_f=2+1+1$ twisted mass fermions on the disconnected contributions to the three point functions entering in studies of hadron structure. Emphasis is given to the nucleon sigma-terms, isoscalar axial charge and first moments of parton distributions for a range of pions masses. The computations are performed using QUDA code implemented on GPUs.

Speaker: Dr Alejandro Vaquero (The Cyprus Institute)

Slides main.pdf

118 Disconnected contribution to the nucleon charges from N_f = 2+1+1 lattice QCD

We calculate the disconnected contribution to the nucleon isoscalar charges of the scalar, axial and tensor channels of light quarks. The calculation has been done by using the Clover valence quarks on the MILC N_f=2+1+1 HISQ lattice at a lattice spacing of 0.12 fm and light quark mass corresponding to the pion mass of 310 MeV. Two-point correlators are evaluated from 60 sources distributed in four timeslices. Disconnected quark loops are estimated by using the truncated solver method with 5000 Gaussian random noise sources. Multigrid inverter is used both for the two-point correlators and the disconnected quark loops. Contamination from the excited states is removed by simultaneously fitting the results of various source-sink separations and operator insertions to the formula including the first excited state. These are applicable to the calculation of other physical observables such as the neutron electric dipole moment and the transverse momentum distribution functions.

Speaker: Dr Boram Yoon (Los Alamos National Laboratory)

Slides Boram_Yoon.pdf

119 Strange quark momentum fraction from overlap fermion

We present a calculation of $\langle x \rangle$ for the strange quark in the nucleon. We adopt overlap fermion action on 2 + 1 flavor domain-wall fermion configurations on the $24^3 \times 64$ lattice. Smeared grid $Z_3$ sources are deployed to calculate the nucleon two-point function with low-mode substitution. Even-odd grid sources and time-dilution technique with stochastic noises are used to calculate the high mode contribution to the quark loop. Low mode averaging is applied to reduce the statistical error of the disconnected insertion calculation.

Speaker: Mingyang Sun (University of Kentucky)

Slides slides.pdf

120 Computing the nucleon sigma terms at the physical point

The nucleon sigma terms are quantities that play a crucial role in phenomenology: among others, they connect the pion-nucleon and the kaon-nucleon amplitudes to the hadron spectrum and they are also relevant for the direct detection of Dark Matter (DM). We present preliminary results for these sigma terms obtained from N_f=2+1 lattice simulations that are performed at five lattice spacings and for pion masses all the way down to its physical value. (Christian Torrero for the Budapest-Marseille-Wuppertal (BMW) collaboration)

Speaker: Dr Christian Torrero (Centre de Physique Théorique (CPT), Aix-Marseille Université)

Slides CTorrero_Lattice_2014.pdf

Hadron spectroscopy and interaction: Parallel 4B

Convener: Dr Hiroshi Ohno (Center for Computational Sciences, University of Tsukuba)

121 Generating 2+1+1 Flavor Mobius Domain Wall Fermion Configurations

The RBC and UKQCD Collaborations are generating 2+1+1 flavor Mobius domain wall fermion configurations with $1/a = 3$ and 4 GeV. To achieve good topological tunneling at these weaker couplings, the gauge action is the Wilson action plus a Dislocation Enhancing Determinant (DED) term. The DED term enhances the probability of gauge fields where toplogy-changing dislocations are present, through the inverse of the effect produced by the Dislocation Suppressing Determinant Ratio (DSDR) we have employed in strong coupling domain wall fermion simulations. Tests and consequences of the DED term will be discussed and some preliminary results of measurements on these lattices will be given.

Speaker: Robert Mawhinney (Columbia University)

Slides talk.pdf

122 The Lambda 1405 is an anti-kaon--nucleon molecule

For almost 50 years the structure of the Lambda(1405) resonance has been a mystery for particle physicists. Even though it contains a heavy strange quark and has odd parity its mass is lower than any other excited spin-1/2 baryon. Before the existence of quarks was confirmed, Dalitz and co-workers speculated that it might be a molecular state of an anti-kaon bound to a nucleon. Although the intervening years have seen considerable effort, there has been no convincing resolution. Here we demonstrate that a new lattice QCD simulation showing that its strange magnetic form factor vanishes, together with a comprehensive Hamiltonian effective field theory analysis of the lattice QCD energy levels, unambiguously establishes that the structure is dominated by a bound anti-kaon--nucleon component. This result clarifies that not all states occuring in Nature can be described within a simple quark model framework and establishes the existence of exotic molecular meson-nucleon bound states

Speaker: Prof. Derek Leinweber (University of Adelaide)

Slides Leinweber_Lambda1405.pdf

123 Multi-channel 1 to 2 matrix elements in finite volume

We derive a model-independent expression for finite-volume matrix elements. Specifically, we present a relativistic, non-perturbative analysis of the matrix element of an external current between a one-scalar in-state and a two-scalar out-state. Our result, which is valid for energies below higher-particle inelastic thresholds, generalizes the Lellouch-Luscher formula in two ways: we allow the external current to inject arbitrary momentum into the system and we allow for the final state to be composed an arbitrary number of strongly coupled two-particle states with arbitrary partial waves (including partial-wave mixing induced by the volume). We also illustrate how our general result can be applied to some key examples, such as heavy meson decays and meson photo production.

Speaker: andre walker-loud (W&amp;M)

Slides Walker-Loud_lattice.pdf

124 Scalar Mesons on the Lattice Using Stochastic Sources on GPU Architecture.

We describe our studies of multi-pion correlation functions computed using stochastic propagators in quenched lattice QCD, harnessing GPUs for acceleration. We find that projecting onto momentum states for the pions becomes enormously expensive and has a poor scaling with the linear extent of the lattice. It is also found that correlations between stochastic propagators appearing in the same diagram, when a single set of random source vectors is used, lead to much larger errors than if separate random sources are used for each propagator. We use L¨uscher’s method and look for the σ in the ππ → ππ channel. The result is that multi-pion correlation functions must be considered, which inevitably involve all-to-all propagators, which are quite expensive and require many inversions. For this reason, GPUs are ideally suited to accelerating the calculation. For this work we have integrated the Columbia Physics System (CPS) and QUDA GPU inversion library, in the case of clover fermions. We describe some other challenges that we have uncovered, in particular getting hit with Amdahl’s law for the tying together and tracing of propagators in our calculations, as well as momentum projections. We have also accelerated these parts of our calculation using GPUs and show some benchmarks.

Speaker: Mr Dean Howarth (Rensselaer Polytechnic Institute)

Slides Howarth_2014.pdf

125 Heavy Meson Spectrum Tests of the Oktay-Kronfeld Action

To achieve smaller heavy-quark discretization errors, the OK action was proposed as an improvement of the Fermilab action. The OK action includes the dimension 6 and 7 operators necessary for tree-level matching to QCD through order 1/m_Q^3 for heavy-light mesons and v^6 for quarkonium. To assess the improvement, we extend previous numerical tests with heavy meson masses by analyzing data generated on a finer lattice with the correct tadpole factors for the c_5 term in the action. We update the analyses of the hyperfine splittings for the rest and kinetic masses and the inconsistency parameter I.

Speaker: Mr Yong-Chull Jang (Seoul National University)

Slides lattice2014_Yong-Chull.pdf

Nonzero temperature and Density: Parallel 4A

Convener: Christian Schmidt

126 Canonical approach to the finite density QCD with winding number expansion

The canonical partition function is related to the grand canonical one through the fugacity expansion. In this talk we perform the fugacity expansion by a method of the hopping parameter expansion in temporal direction: winding number expansion. Since the convergence of our expansion is good only for a small $\kappa$ we concentrate on heavy quark mass region. For a numerical simulation we adopt the improved Wilson fermion with the APE stout smeared gauge links. The grand canonical partition function is made for $N_f=2$ QCD in the imaginary chemical potential region including $\mu=0$. After a derivation of the canonical partition function we study the Lee-Yang zeros of the complexified grand partition function.

Speaker: Dr Yusuke Taniguchi (University of Tsukuba)

Slides lattice2014_tanigchi.pdf

127 Complex Langevin dynamics for SU(3) gauge theory in the presence of a theta term

Recently progress has been made in applying complex Langevin dynamics to nonabelian gauge theories with a sign problem. Here we study the SU(3) gauge theory with a theta therm and present results at real theta.

Speaker: Mr Lorenzo Bongiovanni (Swansea University)

Slides BongioTalk_Lattice2014.pdf

128 Exploring the phase diagram of QCD with complex Langevin simulations

Simulations with a finite chemical potential typically lead to a severe sign problem, prohibiting any standard Monte Carlo approach. For simulations of QCD we use the complex Langevin method, for which we apply adaptive step-sizes and gauge cooling to ensure the convergence. We present preliminary results for heavy quark QCD and explore the application for two dynamical quarks.

Speaker: Mr Benjamin Jaeger (Swansea University)

Slides Jaeger_Lattice14.pdf

129 Towards exact worldline models of lattice gauge theory at finite density

We integrate out all the link variables in the partition function of SU(N) or U(N) lattice gauge theory with the Wilson plaquette action, for arbitrary values of the lattice coupling. The partition function is recast as a Gaussian integral over auxiliary fields, after using suitable Hubbard-Stratonovich transformations. We extend our formalism to lattice gauge theories with staggered fermions at finite temperature and density, and show how to construct the corresponding monomer-dimer-polymer models for arbitrary values of the lattice coupling.

Speaker: Helvio Vairinhos (University of Porto)

Slides Helvio.pdf

130 Solution of simple toy models via thimble regularization of lattice field theory

The sign problem prevents lattice simulations of many models of physical interest. One proposal for evading such problems is the thimble regularization. I will discuss its application to the phi^4 0-dimensional integral, which is a toy model that has been studied for many years as a prototype of complex-valued action and raises several problems within a treatment via complex Langevin; this model can be successfully solved with the thimble approach, though it exhibits a very non trivial structure. I will discuss the details of the thimble structure in this model along with three different algorithms that we have used to get precise numerical results. I will also briefly outline some preliminary results concerning the application of the thimble approach to a Chiral Random Matrix model, which has been recently discussed in the literature and has proved to be problematic for complex Langevin.

Speaker: Dr Eruzzi Giovanni (University of Parma and INFN)

Movie A small avi file with different thimble shapes from \sigma_R>0 to \sigma_R<0

Movie (Animated GIF) movie.gif

Slides lattice14_eruzzi.pdf

Standard model parameters and renormalization: Parallel 4G

Convener: Dr Tanmoy Bhattacharya (Los Alamos National Laboratory)

131 Renormalization constants for $N_{\rm f}=2+1+1$ twisted mass QCD

We summarize recent non-perturbative results obtained for renormalization constants computed in the RI’-MOM scheme for $N_{\rm f}=2+1+1$ twisted mass QCD. Our implementation employs the Iwasaki gauge action and four dynamical degenerate twisted mass fermions. Renormalization constants for scalar, pseudo-scalar, vector and axial operators, as well as for the quark propagator, are computed at three different values of the lattice spacing, two different volumes and several values of the twisted mass. Our method allows for a precise cross-check of the running, because of the particular proper treatment of the hypercubic artifacts. Preliminary results for twist-2 operators are also presented.

Speaker: Dr Savvas Zafeiropoulos (LPC Universite Blaise Pascal CNRS)

Slides zafeiropoulos_lat14.pdf

132 NPR step-scaling across the charm threshold

While Non-Perturbative Renormalisation by itself can be done at any scale, converting it to a perturbative scheme introduces a systematic error decreasing with the scale. In the case of the B_K four quark operator, this is now the dominant error on the MSbar result at 3 GeV. Increasing this scale requires both the access to finer lattices and a correct treatment of the charm effects. We will present a strategy based on step-scaling with a new set of Nf=2+1+1 ensembles generated by the RBC/UKQCD collaboration. In those preliminary results, we will use two different RI/SMOM schemes to estimate the matching error, and we will show that our data gives us good control on chiral and continuum limits.

Speaker: Dr Julien Frison (University of Edinburgh)

Slides slides.pdf

133 Non-perturbative Renormalization of Four-fermion Operators Relevant to B_K with Staggered Quarks.

We present matching factors for the four-fermion operators obtained using the non-perturbative renormalization method (NPR) in RI-MOM scheme for improved staggered fermions on the MILC asqtad lattice (N_f = 2+1). Using 20^3 * 64 lattice (a = 0.12 fm, am_l/am_s = 0.01/0.05), we obtain the matching factor of B_K operator. Also we are in the middle of data analysis on the BSM operators. These results will be used to obtain B_K and the BSM B-parameters. We expect that the matching factor error obtained using NPR is in the level of ~2% which is much smaller than that of the one-loop perturbative matching (~4.4%). We compare NPR results with those of one-loop perturbative matching.

Speaker: Mr Jangho Kim (Seoul National University)

Slides lattice2014_JanghoKim.pdf

134 Nonperturbative renormalization of bilinear operators with Mobius domain-wall fermions in the coordinate space

We study a non-perturbative determination of the renormalization constants of flavor non-singlet quark bilinear operators. The renormalization condition is imposed on correlation functions of bilinear operators in the coordinate space. The results are converted to the value in the MSbar scheme by a perturbative matching. The calculation is done on gauge configurations generated with the Mobius domain-wall fermions at two lattice spacings a = 0.08 and 0.06 fm.

Speaker: Mr Masaaki Tomii (Graduate university for advanced studies)

Slides Tomii.pdf

135 Physical and cut-off effects of heavy charm-like sea quarks

We simulate a theory with two dynamical O(a) improved Wilson quarks whose mass M is close the charm quark mass and at three values of the lattice spacing ranging from 0.066 to 0.038 fm. This theory is a prototype to study the decoupling of heavy quarks. We measure the mass and cut-off dependence of ratios of gluonic observables defined from the Wilson flow or the static potential. The size of the 1/M corrections can be determined and disentangled from the lattice artifacts. The difference with the pure gauge theory is in the percent range when two quarks with a mass of the charm quark are present.

Speaker: Prof. Francesco Knechtli (University of Wuppertal)

Slides lat14_fk.pdf

Theoretical Developments: Parallel 4E

Convener: Prof. Herbert Neuberger (Rutgers)

136 Causal Space-Time on a Null Lattice with Hypercubic Coordination

I discuss the discretization of causal space-times on a topological lattice of events with hypercubic coordination whose links are light-like. Conditions that ensure this lattice is the discretization of a causal manifold are derived. They are encoded by a local topological lattice theory which has a particularly simple and appealing form when null-coframes are represented by spinors.

Speaker: Dr Martin Schaden (Rutgers University)

Slides Schaden_Lattice_2014.pdf Schaden_Null_Lattice_2014.pptx

137 Triviality of $\phi^4_4$ in the broken phase revisited

We define a finite size renormalization scheme for $\phi^4$ theory which in the thermodynamic limit reduces to the standard scheme used in the broken phase. We use it to re-investigate the question of triviality for the four dimensional infinite bare coupling (Ising) limit. The relevant observables all rely on two-point functions and are very suitable for a precise estimation with the worm algorithm.

Speaker: Prof. Ulli Wolff (Humboldt University, Berlin)

Slides talk14.pdf

138 Lattice study on diquark properties

Two point functions of diquarks are calculated in the Landau gauge on the lattice with overlap fermions on 2+1-flavor domain wall fermion configurations. Masses of diquarks with spin 0 and 1 in the color anti-triplet representation are extracted. Pion mass dependence of the mass difference between the bad and good diquarks are studied.

Speaker: Zhaofeng Liu (Institute of High Energy Physics)

Slides lattice2014.pdf

139 Induced QCD with Nc auxiliary bosonic fields

We investigate an alternative lattice discretization of continuum SU(Nc) Yang-Mills theory in which the self-interactions of the gauge field are induced by a path integral over Nc auxiliary bosonic fields which are coupled linearly to the gauge field. In two dimensions there exists an analytic proof that the new discretization reproduces Yang-Mills theory in its non-perturbative continuum limit. We provide numerical evidence that this is also the case in three and four dimensions and that, after a suitable matching between the free parameters, the results of the induced theory agree with results from the ordinary plaquette action up to lattice artifacts. The new discretization is ideally suited to change the order of integration in the QCD path integral to arrive at formulations in which the gauge fields have been integrated out. The resulting theories might be amenable to methods previously used in the infinite-coupling limit, and we briefly discuss a possible dual representation of lattice QCD.

Speaker: Dr Bastian Brandt (University of Regensburg)

Slides talk.pdf

140 Matrix product states for gauge field theories

We consider the matrix product state formalism for the simulation of Hamiltonian lattice gauge theories. To this end, we define matrix product states which are manifestly gauge invariant. As an application, we study 1+1 dimensional one flavor quantum electrodynamics, also known as the massive Schwinger model. We are able to determine very accurately the ground state properties and one-particle excitations in the continuum limit. But we also simulate for the first time the full quantum non-equilibrium dynamics induced by a quench in the form of a uniform background electric field (i.e. the Schwinger pair creation mechanism). Furthermore we study the effects of charge screening and confinement in the vacuum. Finally, we comment on extensions of our method to higher dimensions.

Speakers: Mr Boye Buyens (University Ghent), Dr Karel Van Acoleyen (Ghent University)

Slides Lattice2014.pdf

Vacuum Structure and Confinement: Parallel 4F

Convener: Prof. Edward Shuryak (Stony Brook)

141 Exploring confinement in SU(N) gauge theories with double-trace Polyakov loop deformations

Recent results applying resurgence theory to finite-temperature field theories yield a detailed analytic structure determined by topological excitations. We examine finite-temperature SU(N) lattice gauge theories in light of these results. Double-trace Polyakov loop deformations move through different regions of the confined phase characterized by continuous change in the adjoint Polyakov loop. Lattice models show how the behavior of monopole constituents of calorons can change in the different confining regions. We conjecture that the pure SU(N) gauge theory is close to a special symmetric point where monopole effects give rise to Casimir string-tension scaling.

Speaker: Prof. Michael Ogilvie (Washington University)

Slides Lat_2014_Talk.pdf

142 Magnetic monopole and confinement/deconfinement phase transision in SU(3) Yang-Mills theory

We have proposed the non-Abelian dual super conductivity in SU(3) Yang-Mills (YM) theory for the mechanism of quark confinement, and by using the proposed gauge link decomposition to extract magnetic monopole in the gauge invariant way we presented the evidences in lattice conferences. In this talk, we focus on the dual Meissner effects in view of the magnetic monopole in SU(3) Yang-Mills theory. We measure the chromo-electric and chromo-magnetic flux due to a pair of quark and antiquark source at finite temperature. Then, we measure the correlation function of Polyakov loops and Polyakov loops for various temperatures, and investigate chromo-magnetic monopole current induced by chromo-magnetic flux in both confinement and deconfinement phase. We will discuss the role of the chromo-magnetic monopole in confinement/deconfinement phase transition.

Speaker: Dr Akihiro Shibata (KEK)

Slides monopole-confiement-shibata.pdf

143 Zero modes of overlap fermions, instantons and monopoles

Monopoles are considered that play the very important roles for the color confinement mechanism. University of Kanazawa and Pisa groups have shown a number of studies which support the confinement mechanism due to monopole condensations by the lattice simulations. Instantons that are other topological objects found as solutions of QCD. The close relations to chiral symmetry breaking are theoretically explained, moreover, the relations are revealed by numerical simulations. The purpose of our study is to show that monopoles relate to instantons and chiral symmetry breaking by using the overlap fermions as an analytical tool. To show the relations, first we generate SU(3) configurations for Wilson gauge action. We construct the overlap Dirac operator from link variables of the configurations, solve the eigenvalue problems by using of the subroutines (ARPACK), and find O(80) pairs of eigenvalues and eigenvectors each configurations. We count the number of the zero modes each ensemble. After analytical computations, we confirm that the instanton density is consistent with the instanton liquid model by E. V. Shuryak. Second, we add monopoles and anti-monopoles with several charges to SU(3) configurations for Wilson gauge action by the monopole creation operator which is defined by the University of Pisa group. Third, we fix the maximally abelian gauge. After performed the abelian projection we localize the monopoles on the lattice. We measure the length of monopole loops and the monopole density to confirm that the monopoles are successfully added by the monopole creation operator. The last, we diagonalize the overlap Dirac operator deriving from the configurations which the monopoles are added. We try to quantitatively verify how many the monopoles with charges make the zero modes (instantons) in order to show the relations between them. In my talk, I would like to present our preliminary results.

Speaker: Dr Masayasu Hasegawa (Bogoliubov Laboratory of Theoretical Physics, JINR)

Slides Masayasu.H.Lattice24062014_5.pdf

144 Spectral Flow and Index Theorem for Staggered Fermions

We investigate numerically the spectral flow introduced by Adams for the staggered Dirac operator on realistic quenched gauge configurations in 2D and 4D. We study both the unimproved and the HISQ Dirac operators, and we compare with the case of spectral flow for Wilson fermions. We show that the spectral flow provides a good topological definition of the index, with a clear separation of high and low crossing modes, especially for the HISQ Dirac operator.

Speaker: Dr Eduardo Follana Adin (Universidad de Zaragoza)

Slides follana_lattice14.pdf

145 Topological insulators and the QCD vacuum.

There is considerable evidence, based on large $N_c$ chiral dynamics, holographic QCD, and Monte Carlo studies, that the topological structure of the QCD vacuum consists of discrete quasivacua separated by domain walls across which the local value of the topological $\theta$ parameter jumps by $\pm2\pi$. Topological insulators are condensed matter systems which are bulk insulators with a mass gap but which can transport quantized units of charge via topologically protected boundary states. This is analogous to the QCD vacuum, where the pure glue theory has a bulk mass gap but, when light quarks are included, has Goldstone bosons associated with topological modes of the Dirac operator. As in topological insulators, Goldstone modes in QCD are boundary states on codimension one membranes or domain walls. Following this analogy, the U(1) chiral field in QCD is given by the closed loop integral of a Berry connection around the Brillouin zone in lattice momentum space. This berry phase describes the local polarization of the topological charge membranes.

Speaker: Prof. Thacker H. B. (University of Virginia)

Slides lat14.pdf

Poster session

Conveners: Chulwoo Jung (Brookhaven National Laboratory), Robert Mawhinney (Columbia University), Swagato Mukherjee (BNL)

146 $2+1$ flavor measurement for $\eta$ and $\eta'$ masses using domain wall fermion

The $\eta-\eta'$ mass splitting coming from anomalous effect on U(1) axial currents has been a historical issue. % The QCD gauge field topology with instanton can explain this problem and show consistent result with experimental mass of $\eta'$. % Based on the $2+1$ flavor lattice QCD simulation, previous $\eta-\eta'$ masses study shows about 15\% level of accuracy. % With the advanced computational capability of GPU, we can process more bigger and finer lattice data for higher precision measurement. % In this work, we will show our preliminary $\eta-\eta'$ mass result calculated on $24^3\times 64$ and $32^3\times 64$ Iwasaki gauge lattices corresponding to $a^{-1} = 1.73$GeV.

Speaker: Dr Hyung-Jin Kim (Brookhaven National Laboratory)

147 Baryon resonances coupled to Pion-Nucleon states in lattice QCD

In recent years the study of two particle systems on the lattice has led to excellent results in the meson sector of the QCD spectrum, however baryon resonances remain mostly unexplored. We present an initial study of pion-nucleon systems as decay product of baryon resonances in different channels. The final goal is to extract the resonance parameters from the correlation functions of multi-particle interpolators. All the Wick contributions have to be explicitly evaluated and the consequences of broken symmetries in moving frames are taken into account. We discuss the theoretical setup together with some preliminary results of our trial simulations for nf=2 mass degenerate light quarks.

Speaker: Valentina Verduci (University of Graz)

Slides verduci.pdf

148 Calculation of BSM Kaon B-parameters using improved staggered quarks in N_f = 2+1 QCD.

We present results of the Kaon B-parameters calculated using the HYP-improved staggered quarks on the MILC asqtad lattices. The perturbative matching is done at one-loop level. We extrapolate the data to physical pion mass using the SU(2) staggered chiral perturbation theory. After that, we simultaneously extrapolate results to the continuum (a = 0) and physical sea quark mass. We report our final results evaluated at 2GeV and 3GeV in the $\overline{MS}$ scheme with naive dimensional regularization. And we present error budgets for the B-parameters in the conclusion. This work will lead to a series of constraint equations for the BSM models.

Speaker: Mr Jaehoon Leem (Seoul National University)

Slides lattice2014_jhleem.pdf

149 CL2QCD - Lattice QCD based on OpenCL

In recent years it has been shown that Lattice QCD (LQCD) can benefit enormously from Graphic Processing Units (GPUs), which are well suited for memory bandwidth limited applications. Accordingly, the usage of GPUs in LQCD simulations is still expanding, mainly relying on CUDA, applicable to NVIDIA hardware only. A hardware vendor independent approach is given by the Open Computing Language (OpenCL). We present CL2QCD, a LQCD software based on OpenCL, which has been successfully used for non-zero temperature studies on AMD based clusters. While all mathematical operations are performed in OpenCL, the program logic and the hardware management is carried out in C++. This allows for a clear separation of concerns and, in particular, for a clear distinction of high and low level functionality. Several physical applications have been developed, in this contribution we will focus on the HMC implementation for Wilson and twisted mass Wilson fermions as well as the RHMC for staggered fermions and their performance. In addition we will delve into the concept of unit tests and how it can be applied to LQCD.

Speakers: Mr Alessandro Sciarra (Goethe University, Frankfurt am Main), Mr Christopher Pinke (Institute for Theoretical Physics, Goethe-University Frankfurt am Main)

Poster Lat14_poster_Sciarra_Pinke_part1.pdf Lat14_poster_Sciarra_Pinke_part2.pdf

150 CL2QCD - Lattice QCD based on OpenCL

In recent years it has been shown that Lattice QCD (LQCD) can benefit enormously from Graphic Processing Units (GPUs), which are well suited for memory bandwidth limited applications. Accordingly, the usage of GPUs in LQCD simulations is still expanding, mainly relying on CUDA, applicable to NVIDIA hardware only. A hardware vendor independent approach is given by the Open Computing Language (OpenCL). We present CL2QCD, a LQCD software based on OpenCL, which has been successfully used for non-zero temperature studies on AMD based clusters. While all mathematical operations are performed in OpenCL, the program logic and the hardware management is carried out in C++. This allows for a clear separation of concerns and, in particular, for a clear distinction of high and low level functionality. Several physical applications have been developed, in this contribution we will focus on the HMC implementation for Wilson and twisted mass Wilson fermions as well as the RHMC for staggered fermions and their performance. In addition we will delve into the concept of unit tests and how it can be applied to LQCD.

Speakers: Mr Alessandro Sciarra (Goethe University, Frankfurt am Main), Mr Christopher Pinke (Institute for Theoretical Physics, Goethe-University Frankfurt am Main)

Poster Lat14_poster_Sciarra_Pinke_part1.pdf Lat14_poster_Sciarra_Pinke_part2.pdf

151 Comparative study of topological charge

Comparative study of topological charge is performed. Topological charges are measured by a cloverleaf operator on smoothed gauge configurations. Various types of smoothing techniques are employed. We investigate to what extent each smoothing makes the topological charge an integer. Consistency of the topological charge in the fermionic definition is also examined.

Speaker: Yusuke Namekawa (University of Tsukuba)

152 Condensation in two flavor scalar electrodynamics with non-degenerate quark masses

We explore two flavor scalar electrodynamics on the lattice, which has a complex phase problem at finite chemical potential. By rewriting the action in terms of dual variables this complex phase problem can be solved exactly. The dual variables are link- and plaquette occupation numbers, subject to local constraints that have to be respected by the Monte Carlo algorithm. For the simulation we use a local update scheme. Assigning two different fundamental masses to the two flavors of the underlying model we can achieve a mass splitting between the single-flavor quark-antiquark bound states. We then introduce a finite chemical potential and study the particular characteristics of the systems condensation which we expect due to the mass splitting between the bound states.

Speaker: Mr Alexander Schmidt (Phd)

153 Conformality in twelve-flavor QCD

The spectrum of twelve-flavor QCD has been studied in details by the LatKMI collaboration. Here we present our updated results obtained with the HISQ action at two lattice spacings, several volumes and fermion masses. We emphasize the existence of a flavor-singlet scalar state parametrically light with respect to the rest of the spectrum, first reported in our paper [1]. This feature is expected to be present in theories near the conformal window, but the lattice calculation of such a light state is difficult and requires noise-reduction techniques with large statistics, in order to evaluate disconnected diagrams. Being able to provide a robust observed connection between a light flavor-singlet scalar and near-conformality is an important step towards observing a light composite Higgs boson in walking technicolor theories [2]. Updated spectrum in the other channels is also presented. [1] LatKMI Collaboration, "Light composite scalar in twelve-flavor QCD on the lattice", PhysRevLett.111.162001 [2] LatKMI Collaboration, "Light composite scalar in eight-flavor QCD on the lattice", arxiv:1403.5000

Speakers: Dr Enrico Rinaldi (Physics Division, Lawrence Livermore National Laboratory), Yasumichi Aoki (Nagoya University)

Poster latKMI_Lattice2014_poster_nf12_final_v3.pdf

154 ContinuousBeta

Reverse Monte Carlo, by Mak and Sharma, is a technique that allows for stochastic modification of the action of a lattice theory, while respecting the detailed balance condition of the original action. This modification of the action may permit more efficient evolution of modes with large autocorrelation times. The classic Swendsen and Wang cluster algorithm for the Ising model is in fact a special case of Reverse Monte Carlo, where the action is modified by stochastically deleting certain bonds (i.e. nearest neighbor interaction terms), resulting in cluster decomposition that allows for large scale updates removing critical slowing down. In this work, Reverse Monte Carlo is generalized to a method which allows for continuous change of the couplings in the action. We test the effectiveness of this new approach on the Ising model and an SU(3) pure gauge theory.

Speaker: Mr Arjun Gambhir (College of William and Mary)

155 Correlation functions with Karsten-Wilczek fermions

The explicit breaking of time-reflection symmetry in the Karsten-Wilczek action is hidden in various mesonic correlation functions that are calculated in the quenched approximation. Two underlying discrete product symmetries are discussed, which each allow for enforcement of time-reflection symmetry for correlation functions constructed according to additional symmetry requirements. An additional non-perturbative tuning condition for the relevant fermionic counterterm is demonstrated and a comparison between two independent non-perturbative conditions with boosted perturbation theory is presented.

Speaker: Mr Johannes Heinrich Weber (Technische Universität München)

Poster correlators.pdf

156 Critical behavior and continuum scaling of 3D Z(N) lattice gauge theories

Three-dimensional Z(N) lattice gauge theories are studied numerically at finite temperature for N = 5, 6, 8, 12, 13, 20 and for N_t=2,4,8. For each model the location of phase transitions and their critical indices are determined. The scaling of critical points with N is proposed. The data obtained enable us to verify the scaling near the continuum limit for the Z(N) models at finite temperatures.

Speaker: Alessandro Papa (Universita` della Calabria & INFN-Cosenza)

Poster poster_zn.pdf

157 Current status of $\varepsilon_K$ calculated on the lattice

We present results of $\varepsilon_K$, the indirect CP violation parameter calculated on the lattice combined with various inputs from the experiments. In this analysis we use the lattice results of $B_K$ and $V_{cb}$ for the exclusive channel. In addition, we also use Wolfenstein parameters from the CKM fitters and UT fitters. We find 3.4(3) $\sigma$ difference in the exclusive $V_{cb}$ channel. We report details of this result.

Speaker: Prof. Weonjong Lee (Seoul National University)

Poster wlee.pdf

158 Determination of the mass anomalous dimension for Nf=12 and Nf=9 SU(3) gauge theories

We show the numerical simulation result for the mass anomalous dimension of the SU(3) gauge theory coupled to Nf = 12 fundamental fermions. We use both the step scaling method and the hyperscaling for the Dirac eigenmode to determine the anomalous dimension in the vicinity of the infrared fixed point of the theory. The continuum extrapolation is carefully taken in both analyses. We also show our preliminary result of the anomalous dimension for Nf=9 case.

Speaker: Dr Etsuko Itou (KEK, Japan)

159 Dual simulation of finite density lattice QED at large mass

Using hopping expansion techniques we discuss a partial mapping of finite density lattice QCD to dual variables. After truncation the partition sum has only real and positive contributions also at arbitrary chemical potential, and a Monte Carlo simulation is possible. We discuss the algebraic aspects of the dualization and show some first numerical results.

Speaker: Christof Gattringer (Univ. Graz)

160 Error reduction with all-mode-averaging in Wilson fermion

We report preliminary result of all-mode-averaging technique in Wilson fermion. On two-flavor CLS configurations, we compare the performance to obtain high precision of nucleon form factor and hadronic vacuum polarization function using truncated solver with deflated SAP+GCR algorithm.

Speaker: Dr Eigo Shintani (Mainz University)

Slides poster_lat14_ama.pdf

161 Evidence of BRST-Symmetry Breaking in Lattice Minimal Landau Gauge

By evaluating the so-called Bose-ghost propagator, we present the first numerical evidence of BRST-symmetry breaking in minimal Landau gauge, i.e. due to the restriction of the functional integration to the first Gribov region in the Gribov-Zwanziger approach. We find that our data are well described by a simple fitting function, which can be related to a massive gluon propagator in combination with an infrared-free (Faddeev-Popov) ghost propagator. As a consequence, the Bose-ghost propagator, which has been proposed as a carrier of the confining force in Yang-Mills theories in minimal Landau gauge, presents a 1/p^4 singularity in the infrared limit.

Speaker: Prof. Attilio Cucchieri (University of Sao Paulo)

Poster lattice14.pdf

162 Exploring the phase diagram of Euclidean dynamical triangulations

I present the results of a study of Euclidean dynamical triangulations (EDT) in an attempt to formulate a theory of quantum gravity and to make contact with Weinberg's asymptotic safety scenario. There are two unphysical phases appearing in EDT, neither of which resembles semiclassical gravity. When the phase diagram is enlarged by including a nontrivial measure term a new region of the phase diagram dubbed the "crinkled" region appears. It is shown that this region does not behave like semiclassical gravity, despite initial optimism. Attempts to reconcile this behavior with the results found in functional renormalization group studies that support asymptotic safety are discussed.

Speaker: Jack Laiho (Syracuse University)

163 Exploring the phase structure of 12-flavor SU(3)

We are studying the SU(3) gauge theory with 12 staggered fermions, searching for the endpoint of the line of first-order phase transitions in the mass-beta plane. This endpoint plays an important role in our understanding of the phase diagram of this model. Having found this endpoint with high statistics on a small lattice using unimproved staggered fermions, we are working to find it on larger lattices with improved actions. For an action improved with nHYP-smeared staggered fermions, we discuss the effect of slowly turning off the improvement on the broken shift symmetry phase.

Speaker: Zechariah Gelzer (University of Iowa)

164 Extraction of the isovector magnetic form factor of the nucleon at zero momentum

The extraction of the magnetic form factor of the nucleon at zero momentum transfer is usually performed by adopting a parametrization for its momentum dependence and fitting the results obtained at finite momenta. We present methods that rely on taking the derivative of relevant correlators to extract directly the magnetic form factor at zero momentum without the need to assume a functional form for its momentum dependence. These methods are explored on one ensemble using N_f=2+1+1 Wilson twisted mass fermions.

Speaker: Dr Konstantin Ottnad (University of Cyprus)

Poster poster.pdf

165 Fast evaluation of multi-hadron correlation functions

In recent work, it has been shown that contractions for multi-nucleon systems can be cast in terms of weighted sums of determinants of matrices constructed from quark propagators. For typical correlation functions even for few nucleon systems, the number of such determinants can be very large depending on the complexity of the interpolating fields that are used. We investigate efficient methods for determinant calculations making use of rank-one (and higher-rank) substitutions. Results will be presented that show that these methods provide very significant speedups in calculations of contractions for multi-hadron systems over calculations based on LAPACK routines.

Speaker: Mr Pranjal Vachaspati (MIT)

166 Fermion-bags and a new origin for a fermion mass

Recent developments have shown that the fermion bag approach is a powerful method to solve fermion lattice field theories using Monte Carlo methods. Some sign problems that had remained unsolved earlier can now be solved within this approach. In this work we argue that the fermion bag approach also gives new insight into the mechanism of fermion mass generation. We discuss how chiral condensates can form in most traditional four-fermion models involving staggered lattice fermions although symmetries forbid them. Interestingly, we also discover the existence of models where fermions acquire a mass although the chiral condensate remains zero. In these models fermion masses seem to arise purely due to dynamical reasons rather than due to spontaneous symmetry breaking.

Speaker: Prof. Shailesh Chandrasekharan (Duke University)

167 High-Performance I/O: HDF5 for Lattice QCD

Practitioners of lattice quantum chromodynamics (LQCD) have been some of the primary pioneer users of the state-of-the-art HPC systems, and contribute towards the stress tests of such new machines as soon as they become available. As with all aspects of HPC, I/O is becoming an increasingly specialized component of these systems. In order to take advantage of the latest available high-performance I/O infrastructure, to ensure reliability and backwards compatibility of data files, and to help unify the data structures used in LQCD codes, we have incorporated parallel HDF5 I/O into the SciDAC supported USQCD software stack. Here we present the design and implementation of this I/O framework. The “out-of-the-box” HDF5 implementation outperforms optimized QIO at the 10-20% level, with room for significant improvement with dataset chunking.

Speaker: andre walker-loud (W&amp;M)

168 HISQ inverter on Intel Xeon Phi and NVIDIA GPUs

Speaker: Swagato Mukherjee (BNL)

Slides gpu_mic_poster_swagato.pdf

169 Improved statistics of proton decay matrix element

We report our recent study of proton and neutron decay matrix element with highly improved statistics using all-mode-averaging technique. On 2+1 flavor domain-wall fermion configurations, we obtain accurate proton to pseudoscalar (pion, K and eta) meson transition form factor. In this report we also discuss the comparison with baryon chiral perturbation in physical kinematics and estimate of improvement of GUT prediction.

Speaker: amarjit soni (BNL)

Slides poster_lat14_Ndecay_v2-1.pdf

170 Kaon and D meson semileptonic form factors from lattice QCD

We present calculations of the $K\to\pi,l\nu$ and $D\to\pi,l\nu$ semileptonic form factors at $q^2=0$. These form factors are important for the determination of the CKM matrix elements $\lvert{V_{us}}\rvert$ and $\lvert{V_{cd}}\rvert$ respectively. This work uses the HISQ action for both valence quarks and sea quarks on MILC $N_f=2+1+1$ configurations. We employ twisted boundary conditions to calculate the form factors at zero momentum transfer directly. The $K\to\pi$ results are an update to previously published results with new data at the physical quark mass. The $D\to\pi$ results are preliminary, working at the physical light quark mass at three different lattice spacings down to 0.06 fm.

Speaker: Dr Thomas Primer (University of Arizona)

171 Lattice calculation of neural network of theta neuron

Neurophysics is a relatively new science. We will use quantum field theory to analyze the neural network of theta model. With a special lattice, one can explore the short term memory using lattice field theory calculation. Here we will theoretically show the path integral formalism which can be used to do perturbation theory. Simple lattice simulation will be conducted to compare with the theoretical analysis.

Speaker: Dr Siwei Qiu (National Institute of Health)

172 Lattice QCD code Bridge++ on multi-thread and many core accelerators

We are developing a new code set ``Bridge++'' for lattice simulations. It is aimed to be an extensible, readable, and portable workbench, while it keeps a high performance. Bridge++ covers conventional lattice actions and numerical algorithms. A recent massively parallel cluster system requires a hybrid parallel programing, such as MPI and OpenMP. We also need elaborated programing technique to make use of arithmetic accelerators like GPGPUs and intel Xeon phi. To control accelerator devices, we adopt OpenCL, which provides APIs applicable to wide range of accelerators. We report present status of multi-threading by OpenMP and implementation for accelerator devices.

Speaker: Dr Satoru Ueda (KEK)

Poster satoru_ueda_lattice14.pdf

173 Lepton anomalous magnetic moments from N_f=2+1+1 twisted mass fermions and N_f=2 twisted mass fermions at the physical point

We present our results for the electron, the muon, and the tau anomalous magnetic moments obtained with four dynamical quarks. Performing the continuum limit and an analysis of systematic effects, full agreement with phenomenological results is seen. Additionally, the light quark contributions on the four-flavour sea are compared to the values obtained for N_f=2 physically light quarks. In the latter case different methods to fit the hadronic vacuum polarisation function are tested.

Speaker: Dr Marcus Petschlies (Cyprus Institute / CaSToRC)

Poster poster_gm2_AMA.pdf

174 Leveraging LLVM for Lattice QCD calculations

The Low Level Virtual Machine (LLVM) compiler infrastructure is a promising platform for development of code that features performance portability across a wide variety of architectures. It's widely embraced by HPC industry and academia and high performance code generating backends are available and supported for many relevant architectures such as CUDA, X86-64, PowerPC64 including extensions for the A2Q processor. The QDP-JIT/LLVM library leverages the source- and target-independent code representation known as the LLVM intermediate representation (IR) to generate LQCD kernels from a high level C++ API. Optimizer passes transform the IR in a suitable way for the target platform. We present the QDP-JIT technology and performance numbers resulting from Chroma HMC for a variety of architectures including the new BG/Q support.

Speaker: Dr Frank Winter (Thomas Jefferson National Accelerator Facility)

175 Light glueball masses using multilevel algorithm

Following the multilevel scheme we present an error reduction algorithm for extracting glueball masses from monte-carlo simulations of pure SU(3) lattice gauge theory. We look at the two lightest states viz. the 0^{++} and 2^{++}. Our method involves looking at correlations between large wilson loops and does not require any smearing of links. The error bars we obtain are at the moment comparable to those obtained using smeared operators. We also present a comparison of our method with the naive method.

Speaker: Mr Sourav Mondal (Indian Association for the Cultivation of Science)

Poster poster_lattice2014_final.pdf

176 Neutral B-meson mixing with physical u, d, s, and c sea quarks

HPQCD Collaboration: We will present the first lattice QCD calculation of the mixing parameters f_B\sqrt(B_B) and f_B_s\sqrt(B_B_s) for physical light quark masses. We use 2+1+1 MILC configurations at 3 values of the lattice spacing and with three u/d quark masses going down to the physical value. We use improved NRQCD for the b quarks.

Speaker: Prof. Christine Davies (University of Glasgow)

Poster Bmixing-poster_times.pdf Bmixing-poster_times.pdf

177 Neutron-Antineutron Operator Renormalization

Neutron-antineutron oscillation is a baryon number violating process that is predicted to occur in many theories of physics beyond the standard model. To make quantitative predictions that can be compared to experiment, matrix elements of six-quark effective operators must be computed via lattice QCD and must also be connected to continuum beyond the standard model operators. We present preliminary work on computing operator renormalization and lattice-continuum matching factors to facilitate this connection for neutron-antineutron oscillation operators.

Speaker: Michael Wagman (University of Washington)

178 NRQCD based S- and P-wave Bottomonium spectra at finite temperature from 48^3x12 lattices with Nf=2+1 light HISQ flavors

We present the results of a recent study on the in-medium modification of the spectral properties of Bottomonium S-wave (\Upsilon) and P-wave (\chi_b) states. The medium degrees of freedom are represented by 48^3x12 HotQCD lattices with Nf=2+1 light HISQ flavors, which span the temperature range 140.40(MeV)(= 0.911T_C) < T < 248.63(MeV)(= 1.614T_C). The heavy quarks on the other hand are treated as probes, traveling in the background of the medium fields according to non-relativistic QCD (NRQCD) . Spectral functions are extracted from the NRQCD propagators using a novel Bayesian approach, which is contrasted to the standard Maximum Entropy method. We confirm the finding of previous studies that \Upsilon retains a well defined peak structure even at 1.6TC. Inspection of its mass reveal that medium effects only begin to play a role above T\sim175MeV, while its width appears to grow monotonously. For \chi_b we find that with the new Bayesian method we are able to resolve a ground state peak also up to T=248.6MeV, contrary to the MEM, which suggests ground state melting already at T>205MeV.

Speakers: Dr Alexander Rothkopf (Institute for Theoretical Physics, Heidelberg University, Heidelberg, Germany), Dr Peter Petreczky (Brookhaven National Laboratory - Department of Physics, Upton, USA)

Poster PosterNRQCDFiniteTv1.1.pdf

179 Numerical investigations of Supersymmetric Yang-Mills Quantum Mechanics with 4 supercharges

We report on our non-perturbative investigations of Supersymmetric Yang-Mills Quantum Mechanics with four supercharges. We employed two independent numerical methods. As a first method we used the cut Fock space approach in which one constructs the Hamiltonian matrix in an approximated basis of the Hilbert space and diagonalize it numerically to obtain the energy spectrum. As a second method we implemented the Rational Hybrid Monte Carlo algorithm which allowed us to study our system from a complementary perspective. We present a comparison of results obtained by the two methods for the models with SU(2) and SU(3) gauge groups, focusing on the low-energy part of the spectrum and on the structure of the ground states.

Speaker: Dr Piotr Korcyl (DESY Zeuthen)

Poster poster.pdf

180 Optimization of Lattice QCD Calculation on GTX Titan Black GPU and Xeon Phi Coprocessor

There are new NVIDIA technologies, such as direct parallelism and GPU Direct, which reduce the communication time between GPUs and CPUs. NVIDIA Kepler GPUs also provide new features to improve the memory usage of CUDA codes which allows better performance in memory access, memory allocation, and deallocation. We optimize our conjugate gradient code for staggered quarks to obtain the full performance of the GTX Titan black GPU. We also apply various optimization schemes to the Xeon Phi coprocessor. One is the vectorization of the code by using 512-bit SIMD instructions which is essential to the programming on the Xeon Phi. The other is hybrid programming with MPI and OpenMP. In particular, in the case of OpenMP, threads can share the memory, which can, in principle, reduce the communication overload significantly.

Speaker: Mr Jeonghwan Pak (Seoul National University)

Poster lattice2014_jjome.pdf

181 Overlap Quark Propagator in Coulomb Gauge QCD

The chirally symmetric Overlap quark propagator is explored for the first time in Coulomb gauge. This gauge is well suited for studying the relation between confinement and chiral symmetry breaking. The dressing functions of the quark propagator and the dynamical mass function are evaluated. Chiral symmetry is then artificially restored by removing the low eigenmodes from the Dirac operator. Its effect on the dressing functions is discussed. Via a quark dispersion relation it is shown that confinement is still intact after artificially restoring chiral symmetry.

Speaker: Dr Markus Pak (University of Graz)

182 Partial quenching and chiral symmetry breaking

Partially quenched chiral perturbation theory usually assumes that valence quarks propagating on gauge configurations prepared with sea quarks of different masses will form a chiral condensate as the valence quark mass goes to zero. I present a counterexample involving non-degenerate sea quarks where the valence condensate does not form.

Speaker: Dr Michael Creutz (Physics Department, BNL)

Slides lat14slides.pdf

183 Perturbative and non-perturbative renormalization results of the Chromomagnetic Operator on the Lattice

The chromomagnetic operator mixes with a large number of operators under renormalization. We identify which operators can mix with the chromomagnetic operator, at the quantum level. Even in dimensional regularization (DR), which has the simplest mixing pattern, the chromomagnetic operator mixes with a total of 9 other operators,forming a basis of dimension-five (d=5), Lorentz scalar operators with the same flavor content as the chromomagnetic operator. Among them, there are also gauge noninvariant operators; these are BRST invariant and vanish by the equations of motion, as required by renormalization theory. On the other hand using a lattice regularization further operators with equal or lower dimensionality will mix; choosing the lattice action in a manner as to preserve certain discrete symmetries, a minimul set of 3 additional operators (all with d<5) will appear. In order to compute all relevant mixing coefficients, we calculate the quark-antiquark (2-pt) and the quark-antiquark-gluon (3-pt) Green's functions of the chromomagnetic operator at nonzero quark masses. These calculations were performed in the continuum (dimensional regularization) and on the lattice using the maximally twisted mass fermion action and the Symanzik improved gluon action. In parallel, non-perturbative measurements of the K-π matrix element are being performed in simulations with 4 dynamical (N_f = 2+1+1) twisted mass fermions and the Iwasaki improved gluon action.

Speaker: Mr Marios Costa (University of Cyprus)

184 Probing mesonic and diquark wavefunctions in two color QCD at non-zero baryon density

The properties of the ground state of two-color QCD at non-zero baryon chemical potential mu present an interesting problem in strongly-interacting gauge theory; in particular the nature of the physically-relevant degrees of freedom in the superfluid phase in the high-mu regime still needs clarification. In this study we present evidence for in-medium effects at high mu by studying the wave functions of mesonic and diquark states using orthodox lattice simulation techniques, made possible by the absence of a Sign Problem for the model with Nf=2. Our results show that beyond onset the spatial extent of hadrons decreases with mu, and are consistent with the existence of a dynamically-gapped Fermi surface in this regime.

Speaker: Mr Alessandro Amato (Swansea University)

185 Quark mass dependence of finite temperature phase transitions in QCD with many flavors of Wilson fermions

We investigate the phase transitions of (2+Nf)-flavor QCD, where two light flavors and Nf massive flavors exist, to discuss the electroweak baryogenesis in realistic technicolor scenario. Because an appearance of a first order phase transition at finite temperature is a necessary condition for the baryogenesis, it is important to study the nature of phase transition in the case of massless 2 flavors. Performing simulations of 2-flavor QCD with Wilson fermions and using the reweighting method, we calculate probability distribution functions of the many-flavor QCD. Through the shape of the distribution function, we determine the boundary of the first order region in the parameter space of the light quark mass and heavy quark mass. It is found that the light quark mass dependence of the critical mass of heavy quarks is very small in the region we investigated. From the light quark mass dependence, it is even possible to extract the nature of the transition of massless 2-flavor QCD. Our current result of small dependence suggests that the critical mass of heavy quark remains finite in the chiral limit of 2-flavors and there exists a second order transition region on the line of the 2-flavor massless limit.

Speaker: Dr Shinji Ejiri (Niigata University)

Poster lattice2014pos.pdf

186 Renormalization of parton distribution functions and their moments

Lattice QCD calculations of parton distribution functions have so far been restricted to only their first few Melin moments. Broken rotational symmetry on the lattice introduces unavoidable power divergent mixing of lattice twist-2 matrix elements of different spin that obscures the continuum limit. Here I discuss new options that either avoid power divergent mixing or allow us to perform the subtractions that are needed in order to obtain higher moments.

Speakers: Dr Christopher Monahan (College of William and Mary), Kostas Orginos (College of William and Mary / JLab)

187 Rho mesons in strong abelian magnetic field in SU(3) lattice gauge theory

We calculated correlators of vector and pseudoscalar currents in external strong abelian magnetic field in SU(3) gluodynamics. The masses of charged and neutral mesons with various spins were calculated. We found out that the masses of mesons with zero spin s=0 decreased in increasing magnetic field, but the masses of Rho mesons with nonzero spin increased in the field.

Speaker: Ms Olga Larina (Institute of Theoretical and Experimental Physics)

Slides Larina_Luschevskaya_lattice_2014.ppt

188 Study of the Theta Angle in Scalar QED_2 in a Dual Representation

We study the effect of the theta angle in two dimensional scalar QED. Since the theta term is purely imaginary, it introduces a complex action problem which prevents conventional numerical simulations at non-zero values of theta. This problem is solved by mapping the model to a dual representation, which is real and non-negative, hence suitable for Monte Carlo simulations. We present technical aspects of the reformulation as well as physical results concerning, e.g., the topological charge.

Speaker: Mr Thomas Kloiber (University of Graz)

Poster poster.pdf

189 Targeting the Conformal Window: Determining the Running Coupling

In order to study the transition from conformal to confining behavior of an SU(3) gauge theory, we present the novel idea to simulate a theory with four light and eight heavy flavors. Varying the mass of the heavy flavors, the theory changes from conformal to confining allowing us to demonstrate the walking nature of the running coupling as a function of the mass of the eight heavier flavors.

Speaker: Oliver Witzel (Boston University)

Poster RunCouplingPoster.pdf

190 Test of the Standard Model description of rare $B$ decays using lattice QCD form factors

This poster reviews our recent calculation of $B \to K^*$, $B_s \to \phi$, and $B_s \to K^*$ form factors using nonrelativistic heavy quarks and improved staggered quarks on MILC lattices. These unquenched calculations, performed in the low-recoil kinematic regime, provide a significant improvement over the use of extrapolated light cone sum rule results. We use the form factors along with Standard Model determinations of Wilson coefficients to give theoretical results for several observables. Noting that the experimental measurements for the $B^0 \to K^{*0} \mu^+ \mu^-$ and $B_s \to \phi \mu^+ \mu^-$ branching fractions are smaller at low-recoil than the Standard Model predictions, we perform a fit of the relevant Wilson coefficients using experimental and lattice results. The favored values hint at deviations from the Standard Model that are consistent with fits done by other authors using complementary theoretical and experimental inputs.

Speaker: Dr Matthew Wingate (DAMTP, University of Cambridge)

Slides lattice2014_mbw.pdf

191 Testing the density of states method for the effective center model of QCD

We use the density of states method to compute the observables of the effective center model of QCD at finite density (where the system suffers from a complex phase problem). The density of states method is a reweighting method based on an improved evaluation of histograms for the distribution of states. We test this approach against the results from the dual simulations of the model, where the sign problem is absent.

Speaker: Dr Ydalia Delgado Mercado (University of Graz)

Poster poster_Pascal_Ydalia.pdf

192 The charmonium states X(3872)(1++) and Zc(3900)(1+-) on HISQ lattices

We present preliminary simulation results for the I = 0 charmonium state X(3872)(1++) and the I = 1 charmonium state Zc(3900)(1+-). The study is performed on (2+1+1)-flavor highly improved staggered quark (HISQ) lattices with clover (Fermilab interpretation) charm quarks and HISQ light quarks. Since the X(3872) lies very close to the open charm D-bar-D* threshold, we use a combination of c-bar-c and D-bar-D* interpolating operators. For the Zc(3900) we use a combination of J/psi-pi and D-bar-D* channels. This is the first such study with HISQ light valence quarks. To this end, we describe a variational method for treating staggered quarks that provides for both oscillating and non-oscillating components.

Speaker: Prof. Carleton DeTar (University of Utah)

Slides poster.pdf

193 The effective U(1)-Higgs theory at strong coupling on optical lattices?

We study the U(1)-Higgs model in two dimensions in the strongly coupled regime. The goal is to generate an effective theory where link variables are integrated out, producing 4-field operators. This theory can be matched with the second-order perturbation theory effective Hamiltonian for the Bose-Hubbard model. Such correspondence can then be exploited for building a lattice gauge theory simulator on optical lattices.

Speaker: Alexei Bazavov (University of California/University of Iowa)

194 The mass of the adjoint pion in N=1 supersymmetric Yang-Mills theory

In Monte Carlo simulations of $\mathcal{N}=1$ supersymmetric Yang-Mills theory the mass of the unphysical adjoint pion, which is easily obtained numerically, is being used for the tuning to the limit of vanishing gluino mass. We show how to define the adjoint pion in the framework of partially quenched chiral perturbation theory and we derive a relation between its mass and the mass of the gluino analogous to the Gell-Mann-Oakes-Renner relation of QCD.

Speaker: Prof. Gernot Münster (University of Muenster)

Poster Muenster-Stuewe-Poster

195 The onset of the baryonic density in HD-QCD at low temperature

We use the heavy dense approximation of QCD (HD-QCD) at next-to-leading order (NLO) in the hopping expansion, keeping the full Yang-Mills action. We perform simulations at low temperatures, in the region below 1/3 T_c(\mu=0), and at large \mu, \mu/T above 5. We analyse the structure in the baryonic density and other quantities at the onset. We present data from reweighting (RW) and complex Langevin equation (CLE) calculations for 2 flavours of Wilson fermions, and discuss the results.

Speaker: Ion-Olimpiu Stamatescu (Inst. Theor. Physik, Universitaet Heidelberg)

196 Tuning of the strange quark mass with optimal reweighting

Quark mass reweighting can be used to tune the mass of dynamical quarks. The basic idea is to use gauge field ensembles generated at some bare mass parameters to evaluate observables at different bare sea quark masses. This involves the computation of so called reweighing factors which are given as ratios of fermion determinants. In the case of simulations including the strange quark, reweighting can be used to improve the approach towards physical quark masses. Optimal reweighting strategies combine a change of the strange quark mass with a change of the light quark masses in order to minimize the fluctuations of the reweighting factor. We present numerical test of such strategies for recent CLS2 simulations and a software package for mass reweighting based on openQCD.

Speaker: Dr Björn Leder (University of Wuppertal)

Poster poster.pdf

Wednesday, 25 June

Chiral Symmetry: Parallel 5D

Convener: Prof. Maarten Golterman (San Francisco State University)

197 The Chiral Condensate of One-Flavor QCD and the Dirac Spectrum at $\theta=0$

In a sector of fixed topological charge, the chiral condensate has a discontinuty given by the Banks-Casher formula also in the case of one-flavor QCD. However, at fixed $\theta$ angle, the chiral condensate remains constant when the quark mass crosses zero. To reconcile these contradictory observations, we have evaluated the spectral density of one-flavor QCD at $\theta=0$. For negative quark mass, it becomes a strongly oscillating function with a period given by the inverse space-time volume and an amplitude that increases expoentially with the space-time volume. As we have learned from QCD at nonzero chemical potential, if this is the case, an alternative to the Banks-Casher formula applies, and we will demonstrate that for one-flavor QCD, this results into a continuous chiral condensate. A special role is played by the topological zero modes which have to be taken into account exactly in order to get a finite chiral condensate in the thermodynamic limit.

Speaker: Prof. Jacobus Verbaarschot (Stony Brook University)

Slides lat-14-verbaarschot.pdf

198 Chiral condensate in nf=2 QCD from the Banks-Casher relation

Exploiting the Banks-Casher relation, we present a direct determination of the chiral condensate in two-flavor QCD, computing the mode number of the O(a)-improved Wilson-Dirac operator below various cutoffs. We make use of CLS-configurations with three different lattice spacings in the range of 0.05-0.08 fm and pion masses down to 190 MeV. Our data indicates a finite density of eigenmodes near the origin and hence points to spontaneous chiral symmetry breaking. We extrapolate our results to the continuum and chiral limit to give a result for the chiral condensate.

Speaker: Dr Georg Engel (Universita' Milano-Bicocca)

Slides 2014-Lattice-EngelG.pdf

199 Topological susceptibility from the Dirac spectrum and the Witten-Veneziano formula.

We present our results for the topological susceptibility in the quenched case and attempt a non-perturbative test on the Witten-Veneziano formula. We perform a continuum limit extrapolation of the topological susceptibility computed using spectral projectors. The physical situation of the quenched ensembles was matched to the maximally twisted mass dynamical simulations used to compute the masses of the pseudoscalar mesons. In addition we present a study of the topological charge using spectral projectors including HYP smearing.

Speaker: Dr Elena Garcia Ramos (HU Berlin / DESY-Zeuthen)

Slides LATT2014_EGR.pdf

200 Comparison of different lattice definitions of the topological charge

We present a comparison of different definitions of the topological charge on the lattice, with 2 and 2+1+1 flavours of dynamical twisted mass fermions. We give detailed results at one lattice spacing and also show that the correlation between different definitions increases as one approaches the continuum limit. The investigated definitions are: index of the overlap Dirac operator, spectral projectors, fermionic from disconnected loops, spectral flow of the Hermitian Wilson-Dirac operator and field theoretic with different kinds of smoothing of gauge fields (HYP and APE smearings, gradient flow, cooling). We also show some results on the topological susceptibility.

Speaker: Dr Krzysztof Cichy (DESY Zeuthen)

Slides cichy-lat14.pdf

201 Chiral Properties of Pseudoscalar Meson in Lattice QCD with Domain-Wall Fermion

We study the chiral properties of the pseudoscalar meson in 2-flavors lattice QCD with optimal domain-wall fermion. The gauge ensembles are generated on the $ 24^3 \times 48 $ lattice with the extent in the fifth dimension $ N_s = 16 $, and the plaquette gauge action at $ \beta = 6.10 $, for three sea-quark masses corresponding to the pion masses in the range 265-465 MeV. We calculate the mass and the decay constant of the pseudoscalar meson, and compare our data with the chiral perturbation theory (ChPT). We find that our data is in good agreement with the sea-quark mass dependence predicted by the next-to-leading order (NLO) ChPT, and provides a determination of the low-energy constants $ \bar{l}_3 $ and $ \bar{l}_4 $, the pion decay constant, the chiral condensate, and the average up and down quark mass.

Speaker: Dr Tung-Han Hsieh (Academia Sinica)

Slides latt2014_thh.pdf

Hadron spectroscopy and interaction: Parallel 5B

Convener: Dr Andrew Lytle (TIFR)

202 Nucleon spectroscopy using multi-particle operators

The role of 5-quark operators in extracting the nucleon excited state spectrum via correlation matrix techniques is explored. In particular, the coupling of meson-baryon operators to nucleon resonance states and scattering states is studied. Results are presented for 2+1 flavour dynamical ensembles in both the positive and negative parity channels.

Speaker: Dr Waseem Kamleh (University of Adelaide)

Slides kamleh_lat14.pdf

203 Lattice QCD with 2+1 Flavors and Open Boundaries: First Results of the Baryon Spectrum

Based on CLS simulations with 2+1 flavors and open boundaries we present first results of the baryon spectrum. We report on the status of our effort related to these simulations and the chiral extrapolation to the physical point.

Speaker: Wolfgang Soeldner (Regensburg University)

Slides latt14.pdf

204 Baryon spectrum with Nf=2+1+1 twisted mass fermions

We present results on the masses of the low lying baryons using gauge configurations with $N_f=2+1+1$ flavors of maximally twisted mass fermions. The strange and charm quark masses are tuned to their physical values. We use three values of the lattice spacing, determined from the nucleon mass. Both cut-off effects and volume effects are investigated. We demonstrate that isospin symmetry breaking effects on the baryon masses are small and vanish at the continuum limit. Chiral extrapolations of the masses of the 20 spin-1/2 and 20 spin-3/2 baryons are performed using SU(2) $\chi$PT. After extrapolating to the physical pion mass and taking the continuum limit we find good agreement with the experimentally known baryon masses. Predictions are provided for the masses of the doubly and triply charmed $\Omega$ baryons, that have not yet been measured experimentally.

Speaker: Mr Christos Kallidonis (The Cyprus Institute)

Slides talk_ckallidonis_upload.pdf

205 Excited isovector mesons using the stochastic LapH method

The spectrum of excited isovector mesons is studied using a 32^3 x 256 anisotropic lattice with u,d quark masses set to give a pion mass near 240 MeV. Results in the bosonic isovector nonstrange symmetry channels of zero total momentum are presented using correlation matrices of unprecedented size. In addition to spatially-extended single meson operators, large numbers of two-meson operators are used, involving a wide variety of light isovector, isoscalar, and strange meson operators of varying relative momenta. All needed Wick contractions are efficiently evaluated using a stochastic method of treating the low-lying modes of quark propagation that exploits Laplacian Heaviside quark-field smearing. Level identification is discussed.

Speaker: Prof. Colin Morningstar (Carnegie Mellon University)

Slides Lattice2014.pdf

206 An investigation of meson spectroscopy on isotropic clover lattices at the SU(3) flavor-symmetric point

We present an investigation of the excited meson spectrum at the N_f= 3 point obtained on isotropic clover lattices with a plaquette Wilson gauge action, and a NP-improved clover fermion action, at a lattice spacing of a \simeq 0.08 fm, and compare with corresponding calculations on an anisotropic lattice at fine temporal lattice spacing but a spatial lattice spacing of a_s \simeq 0.125 fm. The methodology adopted follows that employed in the calculation of the spectrum on anisotropic lattices, and we test the efficacy of that approach for isotropic lattices. In particular, we explore the extent to which rotational symmetry for predominantly single-hadron states is realized. By comparison of the energy levels with that obtained using the anisotropic lattice, we obtain an indication of discretization uncertainties in the single-hadron spectrum.

Speaker: David Richards (Jefferson Laboratory)

Slides richards.pdf

Nonzero temperature and Density: Parallel 5A

Convener: Urs Heller

207 Axial U(1) symmetry at finite temperature with Mobius domain-wall fermions

Possible (effective) restoration of the axial U(1) symmetry at finite temperature has attracted a lot of attention in the last few years thanks to the development of the chiral lattice actions and algorithmic improvements. In our previous work we utilized the overlap fermion formulation to show an evidence for a restoration of the axial symmetry above the phase transition. In this work we address the systematics of the previous study by using the Mobius domain-wall fermions that allow for larger-scale simulations while maintaining excellent chiral properties. Different volumes and Ls, the fifth dimension controlling the chirality of the action, and lattice spacings are considered. We study the susceptibilities related to the axial U(1) symmetry, the screening masses, and the spectrum of the Dirac operator (see also A. Tomiya talk).

Speaker: Dr Guido Cossu (KEK)

Slides Guido Cossu Lattice 2014 Talk

208 Effects of near-zero Dirac eigenmodes on axial U(1) symmetry at finite temperature

We investigate the issue of possible restoration of the axial U(1) symmetry at finite temperature, using lattice simulations with the Mobius domain-wall fermion. In this talk, we focus on the effects of near-zero Dirac eigenmodes, which play a crucial role for both SU(2)xSU(2) chiral symmetry restoration and the restoration/breaking of axial U(1) symmetry. Performing simulations at two different volumes, two different quark masses, and reweighting to other masses and to overlap Dirac operators, we study its volume, mass, residual mass dependences.

Speaker: Mr Akio Tomiya (Osaka University)

Slides tomiya_lattice2014_final.pdf

209 Dirac eigenmodes at the QCD Anderson transition

Recently we found an Anderson-type localization-delocalization transition in the QCD Dirac spectrum at high temperature. Using spectral statistics we obtained a critical exponent compatible with that of the corresponding Anderson model. Here we study the spatial structure of the eigenmodes both in the localized and the transition region. Based on previous studies in the Anderson model, at the critical point, the eigenmodes are expected to have a multifractal structure.

Speaker: Prof. Tamas G. Kovacs (Institute for Nuclear Research, Debrecen)

Slides kovacs_tg.pdf

210 Understanding localisation in QCD through an Ising-Anderson model

Above the QCD chiral crossover temperature, the low-lying eigenmodes of the Dirac operator are localised, while moving up in the spectrum states become extended. This localisation/delocalisation transition has been shown to be a genuine second-order phase transition, in the same universality class as that of the 3D Anderson model. The existence of localised modes and the effective dimensional reduction can be tentatively explained as a consequence of local fluctuations of the Polyakov loop, that provide 3D on-site disorder, in analogy to the on-site disorder of the Anderson model. To test the viability of this explanation we study a 3D effective, Anderson-like model, with on-site disorder provided by the spins of an Ising model, which mimics the Polyakov loop dynamics. Our preliminary results show that localised modes are present in the ordered phase, thus supporting the proposed mechanism for localisation in QCD.

Speaker: Dr Matteo Giordano (Institute for Nuclear Research (ATOMKI), Debrecen)

Slides giordano.pdf

211 Chiral transition as Anderson transition

At low temperature the low-lying QCD Dirac spectrum obeys random matrix statistics. Recently we found that above $T_{c}$ the lowest part of the spectrum consists of localized modes that obey Poisson statistics. An interesting implication of this is that as the system crosses $T_{c}$ from above, the spectral statistics at $\lambda=0$ changes from Poisson to random matrix. Here we study this transition and its possible implications for the finite temperature transition of QCD-like theories.

Speaker: Dr Ferenc Pittler (Eotvos Lorand University)

Slides pf_presentation.pdf

Physics beyond the standard model: Parallel 5C

Convener: Dr Kei-ichi Nagai (KMI, Nagoya University)

212 Improved gradient flow for step scaling function and scale setting

The gradient flow renormalized coupling offers a relatively inexpensive way to calculate the step scaling function or the lattice scale, but both applications can be hindered by large lattice artifacts. Recently we introduced an empirical non-perturbative improvement that can remove O(a^2) lattice artifacts. The method is easy to implement and can be applied to any lattice gauge theory of interest both in step scaling studies and for scale setting. In this talk I will briefly review this improvement method and discuss its application to 4, 8 and 12 flavor systems in step scaling function studies and for scale setting in 2+1+1 flavor QCD.

Speaker: Prof. Anna Hasenfratz (University of Colorado Boulder)

Slides Hasenfratz.pdf

213 The gradient flow running coupling in SU2 with 8 flavors

We present preliminary results of the gradient flow running coupling with Dirichlet boundary condition in the SU(2) gauge theory with 8 fermion flavors. Improvements to the gradient flow measurement allow us to obtain a robust continuum limit. The results are consistent with perturbative running in the weak coupling region and show slow running at strong coupling.

Speaker: Dr Jarno Rantaharju (Riken Advanced Institute for Computational Science)

Slides lattice2014.pdf

214 SU(3) gauge theory with 12 flavours in a twisted box

We present our study of the running coupling constant in SU(3) gauge theory with 12 flavours of fermions. In this work we use the method of the step scaling, implemented on lattices with twisted boundary condition. The lattice volumes in this work are 6, 8, 10, 12, 16, 20, and 24. This choice of volumes enables us to investigate the systematic effects in the continuum extrapolation. We discuss in detail the approach of using the Wilson Flow for extracting the coupling constant via the computation of the energy density. In particular, we present results obtained with two different lattice discretisations (clover and the plaquette) of the energy density. Our results shed light on the recent controversy over the infrared behaviour of this gauge theory. Finally, we also briefly comment on the coupling constant computed using the Twisted Polyakov Loop scheme.

Speaker: Prof. C.-J. David Lin (National Chiao-Tung University, Taiwan)

Slides dlin_talk.pdf

215 Four-fermi anomalous dimension with adjoint fermions

The four-fermi interaction can play an important role in models of strong dynamical EW symmetry breaking if the anomalous dimension of the four-fermi operators becomes large in the IR. The anomalous dimension can be computed nonperturbatively using a Schroedinger functional formalism. We present a computation of the four-fermi anomalous dimension for the SU(2) gauge theory with two flavors of Dirac fermions in the adjoint representation.

Speaker: Prof. Luigi Del Debbio (University of Edinburgh)

Slides lat14.pdf

216 Calculating the chiral condensate diagrammatically at strong coupling

We develop a diagrammatic approach for calculating the chiral condensate on the lattice at strong coupling for QCD and related theories with fermions in the symmetric, antisymmetric, and adjoint representations. The approach is inspired by recent work of Tomboulis and earlier work in which the chiral condensate is obtained diagrammatically in the limit of infinite coupling. We calculate the chiral condensate in this limit as a function of the number of colours and fermion flavours and discuss convergence of the approach and sources of error.

Speaker: Dr Joyce Myers (Niels Bohr Institute)

Slides Myers-lattice-2014.pdf

Theoretical Developments: Parallel 5E

Convener: Dr Agostino Patella (CERN and Plymouth University)

217 Prepotential Formulation of Lattice Gauge theories

Within the Hamiltonian formulation of Lattice gauge theories, prepotentials, belonging to the fundamental representation of the gauge group and defined locally at each site of the lattice, enables us to construct local loop operators and loop states. Within this prepotential approach one gets mass gap analytically in some approximations in the weak coupling limit of the theory.

Speaker: Dr Indrakshi Raychowdhury (Institute of Mathematical Sciences, Chennai, India)

Slides 1_indrakshi.pdf

218 Lattice Hamiltonian approach to the Schwinger model

We employ exact diagonalization with strong coupling expansion to the massless and massive Schwinger model. For the massless case, this allows us for a high accuracy continuum limit estimation of the ground state energy and scalar and vector mass gaps with precisions of the order of one part per billion or better. Furthermore, we investigate the chiral condensate and compare our calculations to previous results available in the literature. Oscillations of the chiral condensate which are present while increasing the expansion order are also studied and are shown to be directly linked to the presence of flux loops in the system.

Speaker: Mr Marcin Szyniszewski (Lancaster University, The University of Manchester)

Slides Marcin_Szyniszewski_-_Lattice_2014_presentation.pdf

219 Update on staggered Wilson fermions

An update on our ongoing research on staggered Wilson fermions (a 2-flavor staggered version of Wilson fermions) will be given. Previously we found that this formulation is 4-6 times more efficient than usual Wilson fermions for inverting the Dirac matrix in quenched backgrounds of a 16^3 x 32 lattice at beta=6. Further results for 20^3 x 40 lattices will be reported which reveal that the efficiency increases notably with decreasing lattice spacing at fixed physical volume and also increases slightly with increasing volume at fixed lattice spacing. Construction of meson (and baryon) operators for this formulation will also be described, and numerical results for the pseudoscalar meson spectrum will be presented if they are ready in time.

Speaker: David Adams (Nanyang Technological University)

Slides adams_lattice2014_talk.pdf

220 Pion masses in 2-flavor QCD with $¥eta$ condensation

We investigate some aspects of 2-flavor QCD with $m_u¥not= m_d$ at low-energy, using the leading order chiral perturbation theory including anomaly effects. While nothing special happens at $m_u=0$ for the fixed $m_d¥not=0$, the neutral pion mass becomes zero at two critical values of $m_u$, between which the neutral pion field condenses, leading to a spontaneously CP broken phase, the so-called Dashen phase. We also show that the "topological susceptibility" in the ChPT diverges at these two critical points. We briefly discuss a possibility that $m_u=0$ can be defined by the vanishing the "topological susceptibility. We finally analyze the case of $m_u=m_d=m$ with $¥theta=¥pi$, which is equivalent to $m_u= - m_d=-m$ with $¥theta = 0$ by the chiral rotation. In this case, the $¥eta$ condensation occurs at small $m$, violating the CP symmetry spontaneously. Deep in the $¥eta$ condensation phase, three pions become Nambu-Goldstone bosons, but they show unorthodox behavior at small $m$ that $m_¥pi^2 = O(m^2)$, which, however, is shown to be consistent with the chiral Ward-Takahashi identities.

Speaker: Prof. Sinya Aoki (Kyoto University)

Slides Lat2014.pdf

221 Spectrum of the staggered Wilson Dirac operator in quenched lattice QCD backgrounds

Results for the spectrum of the staggered Wilson Dirac operator in quenched backgrounds (beta = 5.8 and 6) are presented for a range of different lattice sizes up to 16^3 x 32. Significant improvement in the physical branch of the spectrum is observed for the larger lattices. The results are also compared with spectrum results for the usual Wilson Dirac operator in the same backgrounds.

Speaker: Mr Christian Zielinski (Nanyang Technological University, Division of Mathematical Sciences)

Slides lat14_talk.pdf

Vacuum Structure and Confinement: Parallel 5F

Convener: Prof. Harry Thacker (University of Virginia)

222 On the rigid string contribution to the interquark potential

One of the most interesting recent results on the effective string description of Lattice Gauge Theories is the universality of the first few terms of the effective action. This is a direct consequence of the Lorentz invariance of the underlying LGTs and makes this theory much more predictive than usual effective models in particle physics. Besides the well known Nambu-Goto action, one of the combinations allowed by Lorentz symmetry is the so called "rigid string" proposed more that 30 years ago by Kleinert and Polyakov as a candidate to explain confinement in the framework of the dual superconductor scenario. In this talk we discuss a few non trivial properties of this string and evaluate, using the zeta function regularization, the corrections to the interquark potential induced by the extrinsic curvature term contained in the action. We then compare our predictions with a set of high precision simulations of the 3d U(1) LGT and show that the large $\beta$ behavior of the interquark potential is described very well by the rigid string. More precisely we observe, as $\beta$ increases, a smooth cross-over from the usual Nambu-Goto behavior to a rigid string behavior which dominates in the continuum limit. We finally discuss the implications of our results for SU(N) LGTs both in $d=3$ and in $d=4$.

Speaker: Dr michele caselle (Department of Physics, Torino University)

Slides lat2014.pdf

223 Effective string description of the interquark potential in the 3D U(1) Lattice Gauge Theory

The U(1) lattice gauge theory in three dimensions is a perfect laboratory to study the subtle properties of the confining string. On the one hand, thanks to the mapping to a coulomb gas of monopoles, the model can be exactly solved and confinement proven analytically. On the other hand high-precision numerical estimates of Polyakov loop correlators can be obtained via a duality map to a spin model. This allowed us to perform high precision tests of the universal behaviour of the effective string and to find macroscopic deviations with respect to the expected Nambu-Goto predictions. These corrections could be fitted with very good precision by the addition of a contribution proportional to the square of the extrinsic curvature to the effective string action. Such a contribution is allowed by Lorentz invariance and its presence in the infrared regime of the U(1) model was indeed predicted by Polyakov several years ago. Performing our analysis at different values of $\beta$ we were able to show that this term scales as expected by Polyakov's solution and becomes the dominant contribution in the continuum limit. We also discuss the interplay between the extrinsic curvature contribution and the boundary correction induced by the Polyakov loops.

Speaker: Mr Davide Vadacchino (Università degli Studi di Torino - INFN Sezione di Torino)

Slides Vadacchino

224 London penetration depth and coherence length of SU(3) vacuum flux tubes

The transverse profile of the chromoelectric field generated by a quark-antiquark pair in the SU(3) vacuum is analysed within the dual superconductor scenario, then the London penetration depth and coherence length are extracted. The color field is determined on the lattice through a connected correlator of two Polyakov loops measured on smeared configurations.

Speaker: Francesca Cuteri (Università della Calabria, INFN-Cosenza)

Slides cuteri.pdf

225 Anisotropy of the quark anti-quark potential in a magnetic field

We determine the static quark anti-quark potential for QCD at the physical point in the presence of an external magnetic field. The potential is anisotropic, in particular it is steeper in the directions orthogonal to the magnetic field than in the parallel one. The string tension increases (decreases) in the orthogonal (parallel) directions; the absolute value of the Coulomb coupling and the Sommer parameter show an opposite behavior.

Speaker: Mr Francesco Negro (INFN - Sezione di Pisa)

Slides Negro_lat14.pdf

226 The static three-quark potential from the Polyakov loop correlation function

We study the static three-quark potential in SU(3) lattice gauge theory at zero temperature with the Polyakov loop correlation function (PLCF) consisting of three Polyakov loops. Compared to the use of the three-quark Wilson loop, the PLCF allows us to investigate the ground state potential of various three-quark configurations in detail with less systematic effects. We overcome the problem of the statistical errors by employing the multi-level algorithm and obtain remarkably clean signals. We present these results and discuss the possible shape of the confining string for the three-quark system.

Speaker: Dr Yoshiaki Koma (Numazu College of Technology)

Slides lat2014_koma.pdf

Weak Decays and Matrix Elements: Parallel 5G

Convener: Heechang Na (University of Utah)

227 The scalar B meson in the static limit of HQET

I will present results on the scalar B meson ($B_0^*$) sector using $N_f=2$ $\mathcal{O}(a)$-improved Wilson-Clover fermions and the Heavy Quark Effective Field theory at the static limit to describe the b-quark. Since the scalar B meson lies near the B $\pi$ threshold for our simulations set-up, we have implemented meson-meson as well as quark-antiquarks interpolating fields to disentangle the scalar B meson from the two particles states. Using the Generalized Eigenvalue Problem on the full basis, we are able to separate the two levels. Then, we compute the scalar B meson decay constant and the couplings $h$ which parametrizes the Heavy Meson Chiral Perturbation Theory Lagrangian, more precisely the transitions between the $1/2^+$ and $1/2^-$ heavy-light mesons doublets. The couplings $h$ may play a role in the chiral extrapolations when taking the nearest orbital excitations into account in chiral loops.

Speaker: Mr Antoine Gérardin (LPT)

Slides presentation.pdf

228 B meson decay constants and Delta B=2 matrix elements with static heavy and doma in-wall light quarks

Neutral B meson mixing matrix elements and B meson decay constants are calculated. Static approximation is used for b quark and domain-wall fermion is employed for light quarks. The calculations are carried out on Nf=2+1 dynamical ensembles with lattice spacings of 0.086fm and 0.11fm, and a fixed physical spatial volume of about (2.7fm)^3, generated by RBC/UKQCD Collaborations. We employ two kinds of link-smearing and their results are combined in taking a continuum limit. For the matching between the lattice and the continuum theory, one-loop perturbative O(a) improvements are made to reduce discretization errors. We also show statistical improvements by the all-mode-averaging technique.

Speaker: Dr Tomomi Ishikawa (RIKEN BNL Research Center)

Slides Ishikawa_Lattice2014.pdf

229 B-physics with domain-wall light quarks and nonperturbatively tuned relativistic b-quarks

We compute B-meson decay-constants and neutral B-meson mixing using relativistic b-quarks and domain-wall light quarks. We present results for fB, fBs, and their ratio including a complete systematic error budget from an analysis of five sea-quark ensembles with pion masses as light as ~290 MeV and two lattice spacings of a~0.11 and 0.08 fm. We are currently adding data at the physical pion mass using the M"oebius domain-wall ensemble with a~0.11 fm recently generated by the RBC and UKQCD collaboration in order to reduce the dominant systematic uncertainty from the chiral extrapolation. We also report on progress on our calculation of the B-mixing matrix elements.

Speaker: Oliver Witzel (Boston University)

Slides witzel_oliver.pdf

230 Neutral B-meson mixing parameters in and beyond the SM with 2+1 flavor lattice QCD

We present the status of our calculation of the hadronic matrix elements for neutral B-meson mixing with asqtad sea and valence light quarks and using the Wilson clover action with the Fermilab interpretation for the b quark. We calculate the matrix elements of all five local operators that contribute to neutral B-meson mixing both in and beyond the SM. Our analysis includes MILC asqtad ensembles at four different lattice spacings in the range a = 0.045-0.12 fm, and with light sea-quark masses as low as 0.05 times the physical strange quark mass. We perform a combined chiral-continuum extrapolation including the so-called wrong-spin contributions in simultaneous fits to the matrix elements of the five operators. Results for phenomenologically interesting quantities are presented with a complete systematic error budget.

Speaker: Aida El-Khadra (University of Illinois)

Slides axk_lat14.pdf

10:40 Coffee Break

Hadron Structure: Parallel 6D

Convener: Stefan Meinel

231 Suppression of excited-state effects in lattice determination of nucleon electromagnetic form factors

We study the ability of a variety of fitting techniques to extract the ground state matrix elements of the vector current from ratios of nucleon three- and two-point functions that contain contaminations from excited states. Extending our high-statistics study of nucleon form factors, we are able to demonstrate that the treatment of excited state contributions in conjunction with approaching the physical pion mass has a significant impact on the Q^2 dependence of the form factors.

Speaker: Dr Georg von Hippel (University of Mainz)

Slides GvonHippel_lat14_talk.pdf

232 Nucleon electromagnetic form factors from twisted mass lattice QCD

The electromagnetic form factors of the nucleon using twisted mass fermion configurations simulated by the ETM collaboration are presented. These include a gauge field ensemble simulated with two degenerate light quarks yielding a pion mass of around 130 MeV, as well as two ensembles yielding pion masses of 210 MeV and 370 MeV with additional strange and charm sea quarks tuned to their physical mass values. Details of the methods used and systematic errors are discussed, such as noise reduction techniques and the effect of excited state contamination.

Speaker: Dr Giannis Koutsou (The Cyprus Institute)

Slides talk.pdf

233 Systematics analyses on nucleon isovector observables in 2+1-flavor dynamical domain-wall lattice QCD near physical mass

Analyses on possible systematics in some isovector nucleon observables in the RBC+UKQCD 2+1-flavor dynamical domain-wall fermion (DWF) lattice-QCD will be presented.  The reports will be based mostly on the RBC+UKQCD Iwasaki+DSDR ensemble at pion mass of 170 MeV.  The vector charge, axial charge, quark momentum and helicity fractions, and transversity are discussed.  No autocorrelation issue is observed in the vector charge and quark momentum and helicity fractions.  Blocked Jack-knife analyses expose significant growth of estimated error for the axial charge with increasing block sizes that are similar to or larger than the known autocorrelation time of the gauge-field topological charge.  Similar growth is seen in the transversity.  These two observables, however, do not seem correlated with the topological charge.  Related preliminary results obtained jointly by the RBC and LHP collaborations using a RBC+UKQCD Iwasaki ensemble at physical pion mass may also be discussed if relevant.

Speaker: Dr Shigemi Ohta (Institute of Particle and Nuclear Physics, KEK)

Slides 0.pdf

234 Nucleon axial form factors from two-flavour Lattice QCD

We present preliminary results on the axial form factor G_A(Q^2) and the induced pseudo-scalar form factor G_P(Q^2) of the nucleon. The relevant matrix elements were computed on CLS ensembles with N_f =2 non-perturbatively improved O(a) Wilson fermions at three lattice spacings, namely a = 0.050, 0.063, 0.079 fm. These calculations were performed with pion masses ranging from as low as m_pi = 195 MeV to m_pi = 473 MeV with box lengths ranging from L = 2.4 - 4 fm and up to a total of 4000 measurements on each ensemble. A systematic study of the contribution of excited states is performed by analysing the relevant matrix elements at several source-sink separations. Preliminary results on the axial radius r^2_A are also presented.

Speaker: Dr Parikshit Junnarkar (Helmholtz Institut Mainz)

Slides Junnarkar-Lattice2014.pdf

235 Axial and tensor charges of baryons using twisted mass fermions

We present results on the axial charges of the nucleon, the hyperons and charmed baryons using a number of twisted mass fermions ensembles. This includes an $N_f=2$ ensemble with the physical value of the pion mass for which we also show results on the tensor structure of the nucleon.

Speaker: Prof. Constantia Alexandrou (University of Cyprus)

Slides talk.pdf

236 Precision calculations of nucleon charges g_A, g_S and g_T

This talk will present an update on the calculation of iso-vector nucleon charges g_A, g_S and g_T by the PNDME collaboration. The calculations are being done using clover valence quarks on 2+1+1 flavor HISQ lattices generated by the MILC collaboration at multiple values of the lattice spacing, light quark masses and lattice volumes. To extrapolate in the lattice volume, lattice spacing and quark mass, we make simultaneous fits to the data in these three variables and discuss the associated systematic uncertainty in the three charges. Lastly, we will examine how well these estimates, combined with precision measurements of neutron decays, can bound novel scalar and tensor interactions at the TeV scale.

Speaker: Dr Rajan Gupta (Los Alamos National Lab)

Slides Gupta_Lattice_2014.pdf

Hadron spectroscopy and interaction: Parallel 6B

Convener: Christian B. Lang

237 Comparison between two-quark, tetra-quark and molecular states of the sigma meson from lattice QCD

Our purpose is to obtain insights of structure of the sigma meson from lattice QCD. At present we do not reach a conclusive understanding of nature of the sigma meson. Currently it is considered as a usual two-quark state, four-quark states such as a tetra-quark and mesonic molecules or superposition of them. At present we do not reach a conclusive understanding of nature of the sigma meson. Besides, the mixing with glueballs is one of important and interesting ingredients for structure of the sigma meson. Furthermore, a disconnected diagram of the sigma meson plays an important role in the structure of the sigma meson. However, to evaluate the disconnected part of the propagator is not an easy task in lattice QCD calculation. To compute the disconnected part of the propagator, we use the Z2 noise method with the truncated eigenmode acceleration and the time dilution for estimating the all-to-all quark propagators. Here, we compare between two-quark, tetra-quark and molecular states in the sigma meson. An advantage state in the sigma meson will be discussed.

Speaker: Mr Masayuki Wakayama (Nagoya University)

Slides Lattice2014_Wakayama_v4.pptx.pdf

238 Investigation of the tetraquark candidate a_0(980): technical aspects.

The structure of the light-scalar meson a_0(980) is under debate. It might be of quark-antiquark, diquark-antidiquark or mesonic molecule type. We have implemented corresponding interpolating field operators composed of two and of four quarks, as well as operators of two-meson type, to study the structure of a_0(980). The computation of the correlation matrix is rather challenging, because of e.g. closed fermion loops, quark propagation within a timeslice or disconnected pieces. To keep the statistical errors on an acceptable level, one needs to resort to different techniques for different entries and diagrams of the correlation matrix. Here we discuss these techniques in the context of first numerical results.

Speaker: Joshua Berlin (University of Frankfurt)

Slides technicalspects_JBerlin.pdf

239 Investigation of the tetraquark candidate a_0(980): preliminary results

We carry out a study of the light scalar meson a_0(980) employing interpolating field operators of quark-antiquark, diquark-antidiquark, mesonic molecules and two-particle meson operators. Both connected and disconnected quark loops are investigated. We present preliminary results for two ensembles of 2+1 clover fermion gauge configurations generated by the PACS-CS collaboration with pion masses ~300 MeV and ~150 MeV.

Speaker: Dr Abdou Abdel-Rehim (The Cyprus Institute)

Slides abdou_lattice2014_a0_tetraquarks

240 Flavored tetraquark spectroscopy

The very recent confirmation of the Z(4430) charged resonance by the LHCb experiment strongly suggests the existence of QCD bound states with four quarks. We report some preliminary results about hypothetical flavored tetraquark hadrons. Such states are particularly amenable to Lattice QCD studies as their interpolating operators do not overlap with those of ordinary hidden-charm mesons.

Speaker: Dr Andrea Guerrieri (Dipartimento di fisica e INFN Roma "Tor Vergata")

Slides Talk.pdf

241 Search for a bound H-dibaryon using local six-quark interpolating operators

Early results will be presented from a Lattice QCD study seeking a bound H-dibaryon using Nf=2 flavors of O(a) improved Wilson fermions and a quenched strange quark. We solve the generalized eigenvalue problem constructed using a variational basis of interpolators consisting of the two independent local products of six positive-parity-projected quarks with the appropriate quantum numbers, which belong to the singlet and 27-plet irreducible representations of flavor SU(3). To expand this basis, we also independently vary the quark-field smearing. We employ a "blocking" algorithm for the contractions and all-mode-averaging in order to achieve high performance and large statistics. Results will be presented for at least two different pion masses.

Speaker: Dr Jeremy Green (Institut für Kernphysik, Johannes Gutenberg-Universität Mainz)

Slides Green-Hdibaryon.pdf

242 Two-Baryon Systems with Twisted Boundary Conditions

We explore the use of twisted boundary conditions in extracting the nucleon mass and the binding energy of two-baryon systems, such as the deuteron, from Lattice QCD calculations. Using the experimentally determined phase shifts and mixing angles, and utilizing the Luescher method extended to baryonic systems with twisted boundary conditions, we determine the expected energies of the deuteron states over a range of cubic lattice volumes for a selection of twisted boundary conditions. Certain choices of twist angles, as well as selected pair-wise averages, improves the volume dependence of the deuteron binding energy. The set of energy quantizations conditions obtained adds to the previously determined conditions with arbitrary center of mass momenta and is shown to be valuable in constraining the deuteron binding energy and S-D mixing parameter from upcoming lattice QCD calculations of two-nucleon systems at the physical light-quark masses.

Speaker: Dr Zohreh Davoudi (Institute for Nuclear Theory-University of Washington)

Slides Lattice2014.pdf

Nonzero temperature and Density: Parallel 6A

Convener: Heng-Tong Ding

243 Charmonium spectra and dispersion relation with improved Bayesian analysis in lattice QCD

We study the charmonium property at finite temperature and finite momentum in quenched lattice QCD with improved maximum entropy method (MEM). We extend the MEM analysis to the product space of the correlation functions at more than two different momenta to take advantage of more data and the strong correlation among Euclidean correlators with different momenta. We find that this method drastically improves the error of the reconstructed spectral images. We apply this method to analyze the dispersion relation of charmonia at finite temperature.

Speaker: Mr Atsuro Ikeda (Osaka University)

Slides slide.pdf

244 Mesonic spectral functions and transport properties in the quenched QCD continuum

We present new results on the reconstruction of mesonic spectral functions for three temperatures above T_c in quenched QCD. Making use of Clover improved Wilson valence quarks allows for a clean extrapolation of correlator data to the continuum. For the case of vanishing momentum the spectral function is obtained by fitting the data to a well motivated ansatz. In the vector channel for light quarks the electrical conductivity of the hot medium, related to the origin of the spectral function at zero momentum, is computed from the resulting parameters at all three temperatures.

Speaker: Mr Florian Meyer (University of Bielefeld, Germany)

Slides talk_lat2014_fmeyer.pdf

245 Temperature dependence of bottomonium spectral functions

I will present updated results from the FASTSUM collaboration on the bottomonium spectrum at finite temperature from lattice NRQCD on anisotropic $N_f=2+1$ Wilson clover ensembles. Further systematic checks on the reconstruction of the spectral function at high temperatures where few correlator data are available will be discussed. This is relevant to understand the reliability of the observed temperature dependence and the extraction of information on the ground state widths. Preliminary results on higher orbital excitations will be shown.

Speaker: Mr Tim Harris (Trinity College, University of Dublin)

Slides lattice2014.pdf

246 Charmonium spectral functions from 2+1 flavour lattice QCD

Finite temperature charmonium spectral functions in the pseudoscalar and vector channels are studied in lattice QCD with 2+1 flavours of dynamical Wilson quarks, on fine isotropic lattices (with a lattice spacing of 0.057fm), with a pion mass of 545MeV. The highest temperature studied is approximately 1.4Tc. Up to this temperature no significant variation of the spectral function is seen in the pseudoscalar channel. The vector channel shows some temperature dependence, which seems to be consistent with a temperature dependent low frequency peak related to heavy quark transport, plus a temperature independent term at omega>0. These results are in accord with previous calculations using the quenched approximation.

Speaker: Mr Attila Pasztor (MTA-ELTE Lendulet Lattice gauge theory research group/Eotvos University)

Slides talk.pdf

247 Quark mass dependence of quarkonium properties at finite temperature

Quarkonium properties at finite temperature are studied with various quark masses in the range between those for the charm and bottom quarks. Our simulations are performed in quenched QCD with the $O(a)$-improved Wilson quarks on large and fine isotropic lattices at temperatures between about 0.7$T_c$ and 1.4$T_c$. At both vanishing and finite momenta we discuss temperature and quark mass dependence of quarkonium correlation functions and related physical quantities: the quark number susceptibility and the heavy quark diffusion constant.

Speaker: Dr Hiroshi Ohno (Center for Computational Sciences, University of Tsukuba)

Slides lattice2014_ohno.pdf

248 The in-medium heavy quark potential from quenched and dynamical lattice QCD

We present the latest results from two projects focused on determining the temperature dependence of the heavy quark potential from lattice QCD. The real and imaginary part of this real-time potential is obtained from the position and width of the lowest lying peak in the Coulomb gauge Wilson line correlator spectral function [1]. Spectral information is extracted from Euclidean time data using a novel Bayesian approach different from the Maximum Entropy Method, which has been shown to be capable of reproducing the relevant spectral features in mock data tests [2]. Since the determination of the imaginary part is related to the extraction of a spectral width, a large N_\tau is required for a reliable result. Hence the first project deploys anisotropic quenched lattices 32^3xN_\tau (b=7.0 x=3.5) with N_\tau=24,32,40,48,56,64,72,80,96, corresponding to 838.8MeV \geq T\geq 209.7MeV [3]. We find that fits to the Debye mass are in good agreement with prediction from HTL perturbation theory even at rather low temperatures T\gtrsim T_C. The second project provides for the first time a Bayesian spectral function based determination of the heavy quark potential in dynamical lattice QCD [4]. We use the isotropic Nf=2+1 48^3x12 ASQTAD lattices of the HotQCD collaboration [5] and find a clean transition from a confining to a Debye screened Re[V], while the small Nt precludes us from making a quantitative statement about Im[V]. Close agreement between the real part of the potential and the color singlet free energies at high temperatures or small distances is observed. [1] A.R., T. Hatsuda, S. Sasaki Phys.Rev.Lett. 108 (2012) 162001 [2] Y.Burnier, A.R. Phys.Rev.Lett. 111 (2013) 18, 182003 [3] Y. Burnier, A.R. in preparation [4] O. Kaczmarek, A.R. in preparation [5] A.Bazavov et al. PRD85(2010)074501

Speaker: Dr Alexander Rothkopf (Institute for Theoretical Physics, Heidelberg University)

Slides LATTICE2014v1.0_EXPORT.pdf

Physics beyond the standard model: Parallel 6C

Convener: Julius Kuti

249 Phase structure of the N = 1 supersymmetric Yang-Mills theory at finite temperature

The behaviour of supersymmetric theories at finite temperatures differs from that of other theories in certain aspects. Due to the different thermal statistics of bosons and fermions, supersymmetry is explicitly broken for any non-zero value of the temperature. We study the N=1 supersymmetric Yang-Mills theory on the lattice at finite temperatures. This model is the simplest supersymmetric extension of the pure gauge sector of QCD, describing the interactions between gluons and their fermionic superpartners, the gluinos. At zero temperature the theory confines like QCD, and chiral symmetry is spontaneously broken. At high temperatures, deconfinement and chiral symmetry restoration are expected to take place, but it is not known whether these two phase transitions coincide or not. First results on this topic, obtained in numerical simulations, will be presented and discussed.

Speaker: Mr Stefano Piemonte (WWU Münster)

Slides presentazione.pdf

250 Lattice Formulations of Supersymmetric Gauge Theories with Matter Fields

Certain classes of supersymmetric gauge theories, including the well known N=4 super Yang-Mills (SYM) theory, that takes part in the AdS/CFT correspondence, can be formulated on a Euclidean spacetime lattice using the techniques of exact lattice supersymmetry. Great ideas such as topological twisting, Dirac-Kahler fermions, geometric discretization all come together to create gauge theories that are exact-supersymmetric, gauge-invariant, local and doubler-free on the lattice. In this talk we present the lattice formulations of specific classes SYM theories with matter fields in various representations of the gauge group. We hope that such constructions may further motivate the lattice study of technicolor theories, orbifolding and orientifolding in string theories and Corrigan-Ramond limit.

Speaker: Dr ANOSH JOSEPH (Deutsches Elektronen-Synchrotron DESY)

Slides JOSEPH_Lattice14.pdf

251 Loop formulation of supersymmetric Yang-Mills quantum mechanics

The conjectured holographic duality between supersymmetric Yang-Mills quantum mechanics and type IIa string theory in principle allows to probe the physics of certain supergravity black holes by lattice Monte Carlo simulations. In this talk we derive the fermion loop formulation of the 4 and 16 supercharge SU(N) theory on the lattice. The loop formulation naturally separates the contributions to the partition function into its bosonic and fermionic parts and hence provides a way to control a potential fermion sign problem arising from the Pfaffian phase. We present first numerical results for the theories at large values of N and down to low temperatures.

Speaker: Urs Wenger (University of Bern)

Slides lattice2014_wenger.pdf

252 Simulating N=4 Super Yang-Mills

N=4 Yang-Mills may be formulated on the lattice in such a way as to preserve one exact supersymmetry. This has remarkable consequences; the beta function of the lattice theory vanishes at one loop, the moduli space of the theory survives to all orders of perturbation theory and a maximum of two fine tunings are required to take the continuum limit. I will review the formulation and describe the resulting phase diagram of the theory. In certain parts of the phase diagram a lattice monopole phase is found whose existence is driven by the U(1) sector of the theory. I show how this lattice artifact phase can be avoided by the addition of a new term to the lattice action which enforces an approximate projection from a U(N) to an SU(N) gauge group. With the inclusion of this term simulations can be conducted at arbitrarily large 't Hooft coupling.

Speaker: Prof. Simon Catterall (Syracuse University)

Slides lat14.pdf

253 The continuum limit of lattice N=4 super-Yang-Mills

We know from previous studies that the symetries of the twisted Q-symmetric lattice theory are particularly powerful in terms of protecting the long distance effective theory from unwanted renormalizations. Here, it will be shown that rescalings of the lattice fields imply that only two fine-tunings are required, so that the N=4 theory is on a similar footing to clover fermions in lattice QCD. We also provide a blocking scheme that preserves the symmetries. We discuss this in relation to our recent result that restoring any of the discrete R symmetries is sufficient to obtain the correct continuum limit. An early numerical study of this issue is discussed. We conclude with prospects for a Monte Carlo renormalization group involving our blocking scheme.

Speaker: Joel Giedt (Rensselaer Polytechnic Institute)

Slides giedt_lattice.pdf

254 Results from lattice studies of maximally supersymmetric Yang--Mills

I will present results from numerical lattice studies of maximally (N=4) supersymmetric Yang--Mills theory with gauge group SU(2), based on a lattice formulation that exactly preserves one supersymmetry. While the pfaffian of the lattice theory is not manifestly real, direct measurements of the pfaffian show it to be approximately real and positive on all accessible lattice volumes. Studies of the static potential show that the system exhibits coulombic behavior at both weak and strong coupling, with Coulomb coefficients in agreement with leading-order perturbation theory. In addition to these results, I will discuss ongoing studies of gauge groups SU(3) and SU(4), with which we aim to access the large-N limit.

Speaker: David Schaich (Syracuse University)

Slides schaich.pdf

Theoretical Developments: Parallel 6E

Convener: Prof. Stefan Sint (Trinity College Dublin)

255 Conformal Lattice Field Theory on Spherical Manifolds

Lattice radial quantization is a nonperturbative method especially suited to numerically solve Euclidean conformal field theories. Tests are made for the critical surface of the phi 4th theory at the Wilson-Fisher critical point in 3D on R x S2 and in 2D on the Riemann sphere. Simplicial lattice using the Finite Element Methods (FEM) or Regge calculus discretization are need to obtain full conformal symmetry in the continuum. Possible applications to 4D gauge theories are discussed.

Speaker: Dr Richard Brower (Boston University)

Slides Lat14_brower_v1.pdf

256 Blocking versus Sampling

The idea of blocking in configuration space has played an important role in the development of the RG ideas. However, despite being half a century old and having had a huge intellectual impact, generic numerical methods to perform blocking for lattice models have progressed more slowly than sampling methods. Blocking may be essential to deal with near conformal situations. Typically, blocking methods have smaller statistical errors but larger systematic errors than sampling methods. This situation is evolving with recent developments based on the Tensor RG (TRG) method. We report recent results for spin and gauge lattice models obtained with this new method regarding searches for fixed points, calculations of critical exponents and resolutions of sign problems. An interesting model for comparison is the 2-dimensional O(2) model with a chemical potential which has a sign problem with conventional Monte Carlo but allows sampling with the worm algorithm and blocking with various TRG formulations. We compare the efficiency and accuracy of these methods and discuss the possibility of combining them.

Speaker: Yannick Meurice (University of Iowa)

Slides lattice14.pdf

257 Topologically restricted measurements in lattice sigma-models

We consider models with topological sectors and difficulties with their Monte Carlo simulation. In particular, we are concerned with the situation where a simulation has a very long auto-correlation time with respect to the topological charge. In such cases, reliable numerical measurements are only possible within single topological sectors. The challenge is to assemble such restricted measurements to obtain an approximation for the complete result, which corresponds to the correct sampling over the entire set of configurations. We show that under certain conditions this is indeed possible and additionally provides an estimate for the topological susceptibility chi_t. Based on the correlation of the topological charge density, the evaluation of chi_t might be feasible even from data in just one topological sector. Here we present numerical results for these techniques in the framework of non-linear sigma-models by using a cluster algorithm.

Speaker: Dr Urs Gerber (Instituto de Ciencias Nucleares - Universidad Nacional Autonoma de Mexico)

Slides Lattice2014Gerber.pdf

258 Hadron masses from fixed topological simulations: discussion of parity partners and SU(2) Yang-Mills results.

Lattice QCD simulations tend to become stuck in a single topological sector at fine lattice spacing or when using chirally symmetric overlap quarks. In such cases physical observables differ from their full QCD counterparts by finite volume corrections, which need to be understood on a quantitative level. We discuss extensions of existing relations from the literature between correlation functions at fixed topology and hadron masses at unfixed topology. Particular focus is put on disentangling positive and negative parity states, which mix, when the topological charge is fixed. Numerical results are presented for SU(2) Yang-Mills Theory.

Speaker: Arthur Dromard (Goethe Universität, Frankfurt am Main)

Slides lattice_2014_V2.pdf

259 Non-perturbative renormalization of the energy-momentum tensor in SU(3) Yang-Mills theory

We report on an ongoing project of determining non-perturbatively the finite renormalization constants of the energy-momentum tensor in the SU(3) Yang-Mills theory. We compute them by imposing on the lattice suitable Ward Identites at finite temperature and volume in presence of shifted boundary conditions. We present accurate preliminary numerical data for values of the bare coupling g_0^2 ranging for 0 to 1.

Speaker: Dr Michele Pepe (INFN)

Slides Pepe.pdf

260 Topology density correlator on dynamical domain-wall ensembles with nearly frozen topological charge

Global topological charge tends to decorrelate very slowly or to even freeze on fine lattice simulations, while local topological fluctuations are expected to survive and lead to correct physical results as long as the volume is large enough. We investigate this issue on the recently generated configurations including dynamical domain-wall fermions at a=0.08 fm and finer. We utilize the Yang-Mills gradient flow to define the topological charge density operator and calculate its long-distance correlation.

Speaker: Hidenori Fukaya (Osaka University)

Slides 2014JunLattice2014Fukaya2.pdf

Vacuum Structure and Confinement: Parallel 6F

Convener: Dr Eduardo Follana Adin (Universidad de Zaragoza)

261 Testing the Witten–Veneziano mechanism with the Yang–Mills gradient flow on the lattice

We present a precise computation of the topological charge distribution in the SU(3) Yang–Mills theory. It is carried out on the lattice with high statistics Monte Carlo simulations by employing the clover discretization of the field strength tensor combined with the Yang–Mills gradient flow. The flow equations are integrated numerically by a fourth-order structure-preserving Runge–Kutta method. We have performed simulations at four lattice spacings and several lattice sizes to remove with confidence the systematic errors in the second (topological suceptibility χ) and the fourth cumulant of the distribution. In the continuum we obtain χ=185(5) MeV and the ratio between the fourth and the second cumulant R=0.233(45). Our results disfavour the θ-behaviour of the vacuum energy predicted by dilute instanton models, while they are compatible with the expectation from the large-N expansion.

Speaker: Marco Cè (Scuola Normale Superiore, Pisa, Italy and INFN, Sezione di Pisa, Italy)

Slides Lattice2014_Cè.pdf

262 The Gluon Dyson-Schwinger equation of Lattice Landau Gauge

We investigate the exact gluonic Dyson-Schwinger equation of quenched SU(n) lattice gauge theory in Landau gauge and the lattice analog of the Kugo-Ojima confinement criterion.

Speaker: Dr Andre Sternbeck (University of Regensburg)

Slides gluon_dse.pdf

263 Z(N) dependence of the pure Yang-Mills gluon propagator in the Landau gauge near Tc

The Z(N) dependence of the pure Yang-Mills gluon propagator, in the Landau gauge, is investigated at finite temperature for N=3. Special attention will be given to the behaviour near the critical temperature Tc. Our simulations show a complex pattern as expected in a first order phase transition. Furthermore, we identify an order parameter directly associated with the breaking of the SU(3) center symmetry.

Speaker: Dr Paulo Silva (University of Coimbra)

Slides silva.pdf

264 Smearing Center Vortices

We present a method to smear (center projected) Z(2) vortices in order to obtain properties of the original (full) SU(2) configurations. In particular we address the problem that Z(2) configurations cannot be treated with overlap (or chirally improved) fermions due to their lack of smoothness. We develop a method to regain this smoothness and simultaneously maintain the center vortex structure. We verify our method with various gluonic and fermionic observables.

Speaker: Mr Roman Hoellwieser (NMSU)

Slides roman.pdf

265 Centre Vortex Effects on the Overlap Quark Propagator

The fundamental aspects of the QCD vacuum that are responsible for the dynamical generation of mass through chiral symmetry breaking is an ongoing source of debate. We investigate the role of centre vortices in dynamical mass generation using overlap fermions. The exact chiral symmetry that the overlap fermion action possesses yields a distinctive response to the underlying topology of the gauge field, leading to novel results. We study the quark propagator and associated mass function on gauge- field backgrounds featuring the removal of centre vortices as well as on vortex-only backgrounds. The effect of cooling vortex-only backgrounds on the overlap quark propagator is also presented.

Speaker: Mr Daniel Trewartha (University of Adelaide)

Slides Lattice2014Trewartha.pdf

Weak Decays and Matrix Elements: Parallel 6G

Convener: Prof. Aida El-Khadra (University of Illinois)

266 Charm physics with Moebius Domain Wall Fermions

We study the feasibility of using a novel discretisation (Moebius) to directly simulate charm physics within the Domain Wall formalism. We then present results for a range of physical quantities including meson masses as well as decay constants and the dispersion relation of heavy-heavy (eta_c) and heavy-strange (D_s) pseudoscalar mesons. Four extensive sets of tree-level Symanzik pure gauge ensembles with lattice spacing ranging 0.03-0.1fm allow us to perform a continuum limit of the above quantities in a controlled way. Our numerical studies aim to map out the range of simulation parameters where the properties of Domain Wall Fermions known from light quark physics persist.

Speaker: Mr Justus Tobias Tsang (University of Southampton)

Slides lattice14.pdf

267 Charm physics with physical light and strange quarks using domain wall fermions

This talk will provide an overview of RBC/UKQCD's charm project on their 2+1 flavour physical point ensembles using Moebius Domain Wall Fermions for the light as well as for the charm quark. After a brief motivation of DWF as a suitable heavy quark discretisation we will show first results for masses and matrix elements.

Speaker: Dr Andreas Juettner (University of Southampton)

Slides juettner_lat14.pdf

268 Scaling study of an improved fermion action on quenched lattices

We present scaling studies for heavy-quark observables calculated with an O(a^2)-improved fermion action on tree-level Symanzik improved gauge configurations. Lattices of 1/a = 2.0-3.7 GeV with an equal physical volume ~1.6 fm are used. The results are compared with the standard domain-wall and naive Wilson fermions.

Speaker: Mr Yong-Gwi Cho (University of tsukuba)

Slides cho_lattice2014.pdf

269 Charmed and strange pseudoscalar meson decay constants from HISQ simulations

We present final results for decay constants of charmed and strange pseudoscalar mesons, calculated on MILC ensembles with four dynamical quarks. The HISQ action is used for both the valence and sea quarks. A straightforward analysis on the ensembles with physical quark masses, which avoids the need for chiral perturbation theory, is performed first. We report the resulting values for quark mass ratios, as well as an update of our previous result for $f_{K^+}/f_{\pi^+}$. We then fit the lattice data for heavy-light decay constants to expressions derived in staggered chiral perturbation theory. The chiral analysis allows us to use all our data, including ensembles with unphysical sea-quark masses, as well as those with physical masses. This approach makes it possible to achieve small statistical errors and good control of the systematic errors, with final errors at the sub-precent level. A comparison with the results of the straightforward analysis on the physical-mass ensembles is included in the systematic error estimates. We also present continuum-extrapolated results for the decay constants of charmed pseudoscalar mesons evaluated at various values of the light sea-quark mass, which may be useful for normalizing other calculations performed at unphysical mass values.

Speaker: Mr Javad Komijani (Washington University in St. Louis)

Slides Lattice2014_Komijani.pdf

270 Leptonic B and D decay constants with 2+1 flavor asqtad fermions

We present the status of our updated D and B meson decay-constant analysis, based on the MILC Nf=2+1 asqtad gauge ensembles. Heavy quarks are incorporated using the Wilson clover action with the Fermilab interpretation. This analysis includes ensembles at five lattice spacings from a=0.045 to 0.15 fm, and light-quark sea masses down to 1/20 of the strange-quark mass. A complete chiral-continuum extrapolation based on partially quenched staggered chiral perturbation theory is presented, along with a detailed analysis of systematic errors.

Speaker: Prof. Ethan Neil (University of Colorado, Boulder)

Slides eneil-decay-latt14.pdf

271 Matrix elements for D-meson mixing from 2+1 lattice QCD

We present the status of our calculation of the D-meson mixing hadronic matrix elements for all five short-distance operators. We use the $N_{f}=2+1$ asqtad gauge field ensembles generated by the MILC collaboration involving four lattice spacings ranging from 0.12 to 0.045 fm and up/down to strange quark mass ratios as low as 0.05. For the charm quark we use the Sheikholeslami-Wohlert action with the Fermilab interpretation. The valence quarks include the full-QCD point and up to seven partially-quenched points. The matrix elements are extrapolated to the physical point using SU(3) heavy meson staggered chiral perturbation theory. We present preliminary chiral and continuum extrapolated results for all five local operators as well as a full error budget.

Speaker: Chia Cheng Chang (University of Illinois)

Slides ID_376_Matrix_elements_of_D_meson_mixing_Chia_Cheng_Chang.pdf

Thursday, 26 June

Plenary

Convener: Prof. Claude Bernard (Washington University St. Louis)

272 Simulation in Astrophysics

Speaker: Dr Anthony Mezzacappa (Oak Ridge National Laboratory)

Slides Lattice2014_Mezzacappa_v3.pptx

273 Beyond the Standard Model

Speaker: Yasumichi Aoki (Nagoya University)

Slides slide_yaoki.pdf

10:30 Coffee Break

Plenary

Convener: Prof. Weonjong Lee (Seoul National University)

274 FNAL E989 and g-2

Speaker: Dr Brendan Casey (Fermilab)

Slides casey-gm2-lattice2014.pptx

275 Inclusion of isospin breaking effects in lattice simulations

Speaker: Dr Antonin Portelli (University of Southampton)

Slides portelli_lattice2014.pdf

276 Quark masses

Speaker: Dr Francesco Sanfilippo (University of Southampton)

Slides fdm.pdf

Application beyond QCD: Parallel 7C

Convener: Doug Toussaint

277 Beta function of three-dimensional QED

We have carried out a Schrodinger-functional calculation for the Abelian gauge theory with Nf=2 four-component fermions in three dimensions. We find no fixed point in the beta function, meaning that the theory is confining rather than conformal.

Speaker: Dr Benjamin Svetitsky (Tel Aviv University)

Slides Lattice2014.pdf

278 Asymptotic safety on the lattice: the nonlinear O(N) Sigma model

We study the non-perturbative renormalization group flow of the nonlinear O(N) sigma model in two and three space-time dimensions using a scheme that combines an effective local Hybrid Monte Carlo update routine, blockspin transformations and a Monte Carlo demon method. In two dimensions our results verify perturbative renormalizability. In three dimensions, we determine the flow diagram of the theory for various N and different truncations and find a non-trivial fixed point, which indicates non-perturbative renormalizability. It is related to the well-studied phase transition of the O(N) universality class and characterizes the continuum physics of the model. We compare the obtained renormalization group flows with recent investigations by means of the Functional Renormalization Group.

Speaker: Mr Daniel Körner (FSU Jena)

Slides talk.pdf

279 Hybrid Monte Carlo simulations of Graphene in presence of vacancies

Tight-binding model of Graphene with vacancies in crystal structure was studied within the framework of Hybrid Monte Carlo simulations. Antiferromagnetic ordering is observed in the vicinity of the vacant sites. Mass gap is extracted from the calculations of the two-point Euclidean Green function. It is demonstrated that even a relatively small concentration of vacancies can lead to opening a mass gap in monolayer Graphene.

Speaker: Dr Maksim Ulybyshev (Regensburg University)

Slides presentation_ulybyshev.pdf

280 Monte-Carlo study of the phase transition in the AA-stacked bilayer graphene

Tight-binding model of the AA-stacked bilayer graphene with screened electron-electron interactions has been studied using the Hybrid Monte Carlo simulations on the original double-layer hexagonal lattice. Instantaneous screened Coulomb potential is taken into account using Hubbard-Stratonovich transformation. G-type antiferromagnetic ordering has been studied and the phase transition with spontaneous generation of the mass gap has been observed. Dependence of the energy gap on the on-site electron-electron interaction is examined. It is found, that the energy gap vanishes at some finite value of the on-site interaction potential, which differs from the dependence, predicted by the mean-field approximation.

Speaker: Mr Alexander Nikolaev (Far Eastern Federal University)

Slides A.A.Nikolaev_talk_presentation.pdf

281 Hybrid-Monte-Carlo simulation of the tight-binding model of graphene with partially screened Coulomb interactions

We report on the status of our ongoing Hybrid-Monte-Carlo simulations of the tight-binding model for the electronic properties of graphene, using a realistic potential for the two-body interactions. Our short-range interactions thereby include the partial screening due to electrons in higher energy states from ab initio calculations based on the constrained random phase approximation [T.O.Wehling et al., Phys.Rev.Lett. 106, 236805 (2011)]. We also include a phenomenological model which describes the transition to the unscreened bare Coulomb interactions of graphene at half filling in the long-wavelength limit. We present up-to-date results on the transition from the semimetal to an antiferromagnetic insulating phase and outline a number of additional problems which will be addressed using our code.

Speaker: Dr Dominik Smith (TU Darmstadt)

Slides talk_smith.pdf

282 Lattice path integrals for relativistic and non-relativistic many-body quantum systems

New formulation of path integrals for relativistic quantum systems will discussed. Influence of the relativistic effects on the properties of quantum systems will be studied by means of the Monte Carlo method. A generalization of this approach to the case the path integral quantization of the Born-Infeld field theory will also discussed.

Speaker: Dr Oleg Pavlovskiy (Moscow State University)

Slides pavlovskiy.pdf pavlovskiy.ppt

283 Numerical simulation of graphene in an external magnetic field

The results of numerical simulation of graphene effective field theory in external magnetic field are presented. The numerical simulation is performed using noncompact (3+1)-dimensional Abelian lattice gauge fields and (2+1)-dimensional staggered lattice fermions. The dependences of fermion condensate and conductivity on the dielectric permittivity of the substrate for different values of external magnetic field are calculated. It is found that magnetic field shifts insulator-semimetal phase transition to larger values of the dielectric permittivity of the substrate. The phase diagram of graphene in external magnetic field is drawn.

Speaker: Mr Semen Valgushev (Institute for Theoretical and Experimental Physics)

Slides presentation_graphene.pdf

Hadron Structure: Parallel 7D

Convener: James Zanotti

284 Electric polarizability of neutral hadrons from dynamical lattice QCD ensembles

Knowledge of the electric polarizability is crucial to understand the interactions of hadrons with electromagnetic fields. The neutron polarizability is very sensitive to the quark mass and is expected to diverge in the chiral limit. Here we present results for the electric polarizability of the neutron, neutral pion, and neutral kaon on eight ensembles with nHYP-smeared clover dynamical fermions with two different pion masses (227 and 306 MeV). These are currently the lightest pion masses used in polarizability studies. For each pion mass we compute the polarizability at four different volumes and perform an infinite volume extrapolation for the three hadrons. Along with the infinite volume extrapolation we conduct a chiral extrapolation for the kaon polarizability to the physical point. We compare our results for the neutron polarizability to predictions from chiral perturbation theory.

Speaker: Mr Michael Lujan (The George Washington University)

Slides mlujan_lattice_2014.pdf

285 Perturbative reweighting, dilution, and low mode substitution for sea quark contribution to the neutron polarizability

The contribution of the sea quark charges is a large uncertainty in lattice calculations of hadron polarizabilities; we present an update in our use of perturbative reweighting in the quark charge to address this issue. The difficult aspect of this calculation is the stochastic estimation of the weight factor expansion coefficients. We use aggressive (large-N) dilution, consisting of body-centered (hyper)cubic spatial dilution in addition to spin/color dilution, to minimize the contribution of large near-diagonal elements to the estimator variance. We will present results from this technique applied to our smallest-volume ensemble. For a larger ensemble we have developed a variant of low-mode subtraction in which low modes of \gamma_5 D are treated separately; this further reduces the estimator variance by an order of magnitude. We will discuss the various stochastic estimator improvement techniques and present in-progress results from the new calculation.

Speaker: Dr Walter Freeman (George Washington University)

Slides latt2014.pdf

286 Background field method and nonrelativistic QED matching

We discuss the resolution of inconsistencies between the background field method in lattice QCD and the effective field theory matching conditions. Lack of on-shell conditions in lattice QCD with time-dependent background fields requires that operators related by equations of motion in the effective field theory should be retained in the action to describe the Green's function correctly. As a concrete example, we perform a robust non-relativistic expansion of the relativistic QED action for scalar and spin-half hadrons under uniform electromagnetic fields, and obtain the nonrelativistic QED matching conditions including the equation-of-motion operators. For a scalar hadron, this result is also supported by the matching at the level of the Green's function. The method is extended to treat the proton in uniform electric and magnetic fields, where Landau levels are addressed in the latter case to allow determination of the magnetic polarizability.

Speaker: Dr JONG-WAN LEE (City College of New York)

Slides lattice2014_JWLEE.pdf

287 Vacuum alignment and lattice artifacts

When a subgroup of the flavor symmetry group of a gauge theory is weakly coupled to additional gauge fields, the vacuum tends to align such that the gauged subgroup is unbroken. At the same time, the lattice discretization typically breaks the flavor symmetry explicitly, and can give rise to new lattice-artifact phases with spontaneously broken symmetries. We discuss the interplay of these two phenomena, using chiral lagrangian techniques. Our main example is two-flavor Wilson QCD coupled to electromagnetism. We will briefly touch on theories with staggered fermions and composite Higgs models as well.

Speaker: Maarten Golterman (San Francisco State University)

Slides golterman_lat14.pdf

288 Electromagnetic structure of charmed baryons in Lattice QCD

The electromagnetic form factors of \Sigma_c, \Xi_cc, \Omega_c and \Omega_cc baryons are computed and their electric and magnetic charge radii as well as their magnetic moments are extracted in 2+1 flavor Lattice QCD. Extrapolated physical point results show that the charge radii and magnetic moments are smaller compared to those of, e.g., proton. Investigating the individual quark contributions suggests that the existence of the heavy charm quark is responsible of such decrease.

Speaker: Kadir Utku Can (Tokyo Institute of Technology)

Slides utku_can_id308.pdf

289 Radiative Physics on the Lattice using Distillation

We present a progress update on an ongoing calculation aimed at extracting photocouplings in the light-quark sector from radiative matrix elements computed using lattice QCD. These couplings drive the rate of photo production of mesons, of particular interest are exotic and hybrid mesons which while present in lattice calculations have yet to be observed experimentally. The use of distillation in conjunction with a large variational basis of interpolating operators allows for efficient extraction of signals from three-point functions making such calculations possible. Preliminary results for excited state light quark transition form factors will be presented.

Speaker: Mr Christian Shultz (Old Dominion University)

Slides RadTranLattice2014.pdf

290 Electromagnetic matrix elements for excited Nucleons

Over the past decade there has been significant experimental interest into the electromagnetic excitation of nucleon resonances and their underlying structure. Given the large body of data that now exists, it is interesting to consider the expectations presented by QCD. Correlation matrix techniques present us with the ideal approach to extracting matrix elements of hadronic excitations. Following our recent success in identifying the underlying structure of the Lambda(1405) using this approach, we now consider the nucleon sector. In this talk we shall outline the method and present first results for the low-lying nucleon excited state spectrum in the positive and negative parity channels.

Speaker: Mr Benjamin Owen (University of Adelaide)

Slides latt_2014_ben.owen.pdf

Hadron spectroscopy and interaction: Parallel 7B

Convener: Prof. Ting-Wai Chiu (National Taiwan University)

291 An improved study of the excited radiative decay $\Upsilon(2S) \to \eta_b(1S)\gamma$ using lattice NRQCD

Recently Lewis and Woloshyn's exploratory study using lattice NRQCD to study the radiative decay $\Upsilon(2S) \to \eta_b(1S) \gamma$ found that next-to-leading order ($v^6$) contributions were large compared to the leading order ($v^4) result. We explain this suppression of the $v^4$ term using a simple potential model. We then present our lattice QCD results obtained with three lattice spacings and high statistics. We employ improved actions, twisted boundary conditions, 1-loop perturbative matching, and Bayesian fitting methods. We conclude that lattice NRQCD can be used to accurately calculate this and other radiative bottomonium decay rates.

Speaker: Mr Ciaran Hughes (DAMTP, University of Cambridge)

Slides CiaranHughesLattice14.pdf

292 Determining Sigma - Lambda mixing

SU2 isospin breaking effects in hadron octet and decuplets are due to a combination of up and down quark mass differences and electromagnetic effects. Usually these masses difference are small. Between the Sigma and Lambda the splitting is much larger due to mixing between these states. We determine the QCD mixing matrix and hence find the mixing angle and mass splitting. Provided the average quark mass is kept constant, the expansion coefficients in our procedure can be determined from computationally cheaper simulations with mass degenerate sea quarks and partially quenched valence quarks.

Speaker: Dr Roger Horsley (University of Edinburgh)

Slides talk_rhorsley_lat14.pdf

293 Free-form Smeared Bottomonium Correlation Functions

Gauge-invariant sources with a hydrogen wave function shape are constructed for bottomonium two-point correlation functions using the free-form smearing technique. The bottomonium spectrum is extracted from free-form smeared correlation functions. Results are compared with conventional smearing techniques.

Speaker: Mr Mark Wurtz (York University)

Slides wurtz_lattice_2014.pdf

294 Omega-Omega interaction from 2+1 flavor QCD

We report our results of central potential between two Omega baryons from 2+1 flavor full Lattice QCD simulation.In the past studies, there is a possibility that some decuplet baryons have a bound state. However, almost all decuplet baryons are unstable due to decays via the strong interaction. An exception is the Omega decuplte baryon, which is stable against the strong decays, so its interaction is suitable to be investigated. It is, however, still difficult to investigate the Omega-Omega interaction experimentally due to its short-life time via weak decays.Therefore, the lattice QCD study for the Omega-Omega interaction is necessary and important. We present results obtained by the extension of the HAL QCD method to the system of two decuplet baryons. Our numerical results are obtained from 2+1 flavor full QCD gauge configurations at $L \sim 2.9 $fm $m_\pi \sim 701 $MeV $ and m_\Omega\sim 1966 &MeV, generated by the PACS-CS Collaboration. We find that the Omega-Omega interaction is strong attractive, but it's not strong enough to make a bound state at out simulation set up.

Speaker: Mr Masanori for HAL QCD Coll Yamada (University of Tsukuba)

Slides yamada_Lattice2014.pdf

295 Quark mass dependence of three-nucleon forces in lattice QCD

Recently, the determination of three-nucleon forces attracts a great deal of interest in light of their role in nuclear and astrophysical phenomena such as EoS of nuclear matter and the structure of the neutron star core. In this talk, we present the lattice QCD calculation of three-nucleon forces utilizing the time-dependent HAL QCD method. In particular, we study the quark mass dependence of three-nucleon forces from lattice simulations with Nf=2 clover fermion action at m(pi) = 0.76, 0.93, 1.13 GeV.

Speaker: Dr Takumi Doi (RIKEN)

Slides doi.pdf

296 A study of scattering in open charm channels

Preliminary results from a study of $DK$ and $D\pi$ scattering are presented using a set of anisotropic $N_f=2+1$ dynamical gauge field configurations generated by the Hadron Spectrum Collaboration. The variational method with a large operator basis is used in two lattice volumes to determine the excitation spectra of open charm mesons with the relevant scattering states containing one valence charm quark. Scattering observables and resonance parameters for open charm states are also discussed.

Speaker: Prof. Sinead Ryan (Trinity College Dublin)

Slides SRyan.pdf

Nonzero temperature and Density: Parallel 7A

Convener: Szabolcs Borsanyi

297 Thermodynamics in the fixed scale approach with the shifted boundary conditions

The fixed scale approach has various advantages to calculate the QCD equation of state on lattices. In this approach a series of temperatures are realized with single coupling parameters. Therefore zero temperature subtractions are common, and conditions for the line of constant physics are automatically satisfied. We test the fixed scale approach to study thermodynamics of SU(3) gauge theory using the shifted boundary conditions, which can largely increase the number of possible temperatures while keeping the advantages of the fixed scale approach. The simulations are performed with 32^3 x Nt lattices at beta=6.0. Calculations at 80 temperature are investigated with the single coupling parameter by using various boundary shifts at Nt=4,5,6,7,8 lattices. We present the results of the trace anomaly, and the transition temperature determined by the plaquette susceptibility. We also found that the boundary condition reduces lattice artifacts in the equation of state numerically.

Speaker: Takashi Umeda (Hiroshima University)

Slides lattice2014_umeda.pdf

298 Multipoint reweighting method and beta-functions for the calculation of QCD equation of state

We discuss the reweighting method aiming numerical studies of QCD at finite density, in which the Monte-Carlo method cannot be applied directly. One of the most important problems in the reweighting method is the overlap problem. To solve the problem, we propose the following reweighting method: simulations are performed at several simulation points and the analysis is done combining all data. We explain the method and discuss the improvement of the overlap problem. As an application of the multipoint reweighting method, we compute the meson masses as continuous functions of beta and hopping parameters (kappa). Then, lines of constant physics in the (beta, kappa) space are determined, and the derivatives of the lattice spacing with respect to beta and kappa are calculated along the lines of constant physics, which are needed for the calculation of the equation of state.

Speaker: Mr Ryo IWAMI (Niigata University)

Slides lat14iwami.0621forslide.yobi3.pdf

299 QCD Thermodynamics With Continuum Extrapolated Wilson Fermions

We study 2+1 flavour QCD thermodynamics using Wilson fermions in the fixed scale approach. The temperature dependence of the renormalized chiral condensate, quark number susceptibility and Polyakov loop is determined at three pion masses down to 280~MeV. Four lattice spacings are used allowing for a controlled continuum limit.

Speaker: Mr Norbert Trombitas (Eotvos Lorand University)

Slides N. Trombitas' talk

300 Recent results on the Equation of State of QCD

I will review results for the Equation of State of QCD, in particular I will give an update on our calculation that includes a dynamical charm quark.

Speaker: Dr Stefan Krieg (Forschungszentrum Juelich GmbH/Wuppertal University)

Slides Krieg.pdf

301 The QCD Equation of State

The HotQCD Collaboration has calculated the equation of state in 2+1 flavor QCD at zero net baryon density using the Highly Improved Staggered Quark (HISQ) action. The strange quark mass was set to its physical value and the light (up/down) quark masses used correspond to a pion mass of 160 MeV in the continuum limit. Lattices with temporal extent Nt=6, 8, 10 and 12 were used, and the cutoff effects for Nt>6 were observed to be quite small. For temperatures in the range 130 MeV < T < 400 MeV continuum extrapolations were performed. We will discuss errors and compare our results with others in the literature.

Speaker: Tanmoy Bhattacharya (LANL)

Slides BhattacharyaHotQCD.pdf

302 The QCD Equation of State at order $\mu_B^4$

Hydrodynamic models of heavy-ion collisions have increasingly begun to rely on lattice results for the Equation of State. While the lattice has the advantage of being a first-principles approach to QCD, the notorious sign problem prevents a direct determination of the equation of state and other thermodynamic observables at finite chemical potential $\mu_B$. Quark number susceptibilities allow us to extrapolate the equation of state in a controlled way to small values of $\mu_B$ based on calculations at $\mu_B=0$. Such an extrapolation is necessary in order to accurately describe the results from the beam energy scan at RHIC and from the LHC where typically $\mu_B/T=0.1$-4, depending upon the energy of the beam. In our talk, we will present results from a high-statistics calculation of all the Taylor coefficients upto sixth order in a $(\mu_B,\mu_Q,\mu_S)$-expansion of the pressure. Our calculation allows us to extrapolate, for the first time, the equation of state on the freezeout curve upto $\mathcal{O}(\mu_B^4)$ while our sixth-order results show that the truncation error is not more than a few \% upto $\mu_B/T\sim1.5$. Thus our equation of state should be useful in describing both the LHC results as well as results from RHIC beam energy scan down to $\sqrt{s}\sim$20 GeV. We will also use our results to construct the isentropic equation of state for strangeness-neutral systems. Our lattice QCD calculations make use of the gauge ensembles generated using the HISQ action. Our lattices sizes range from $6\times24^3$ to $12\times48^3$ and the pion mass ($\sim$160 MeV) is nearly equal to its physical value while the strange quark is at exactly its physical value.

Speaker: Dr Prasad Hegde (Central China Normal University)

Slides lat2014_hegde.pdf

303 The QCD Phase Transition with Three Physical-Mass Pions

On behalf of the HotQCD collaboration, I present results from the first lattice study of the QCD phase transition using chiral fermions and physical quark masses. With domain wall fermions, the dislocation suppressing determinant ratio (DSDR), a temporal Euclidean extent of 8 sites, and spatial extents of at least 4 and up to 11 fm, we have computed the disconnected chiral susceptibility for several temperatures between 130 and 200 MeV and found a pronounced peak, the position and height of which depend sensitively on the quark mass. We find no metastability in the peak region and no significant change in the peak height upon increasing the spatial extent from 5 to 10 fm, strong evidences that the transition is an analytic crossover. We derive a pseudo-critical temperature of 155(1)(8) MeV and find that while chiral symmetry is fully restored above 164 MeV, anomalous $U(1)_A$ symmetry breaking is substantial until roughly 196 MeV. In addition, I present preliminary results for our latest calculation with a temporal extent of 12 sites, aimed at quantifying finite lattice spacing effects.

Speaker: Dr Chris Schroeder (LLNL)

Slides schroeder_lattice2014_v3.pdf

Standard model parameters and renormalization: Parallel 7G

Convener: Dr Christopher Monahan (College of William and Mary)

304 Towards a new determination of the QCD Lambda parameter from running couplings in the three-flavour theory

We review our new strategy and current status towards a high precision computation of the Lambda parameter from three-flavour simulations in QCD. To reach this goal we combine specific advantages of the Schroedinger functional and gradient flow couplings.

Speaker: Dr Patrick Fritzsch (Humboldt University Berlin)

Slides fritzsch_Lat14.pdf

305 A Feynman-Hellmann approach to nonperturbative renormalization of lattice operators

Renormalization factors are needed to related lattice quantities to their corresponding continuum counterparts. In order to renormalize singlet observables one has to include connected and disconnected diagrams. Especially, the disconnected contributions are very difficult to calculate using the standard three-point function technique. The Feynman-Hellmann method provides the possibility to calculate the renormalization factors from two-point functions from which much better signals can be extracted. However, one has to simulate with additional modified actions. In this talk we present first results for the Nf=2+1 SLiNC action. We compute the renormalization factors of selected local operators for the non-singlet and singlet cases.

Speaker: Dr Holger Perlt (Leipzig university)

Slides Talk_Perlt_Lattice2014.pdf

306 Determination of \(c_{\rm sw}\) in \(N_f=3+1\) Lattice QCD with massive Wilson fermions

We develop a strategy for the non-perturbative determination of the O(\(a\))-improvement coefficient \(c_{\rm sw}\) for Wilson fermions with massive sea quarks. The improvement condition is defined via the PCAC relation in the Schrödinger functional. It is imposed along a line of constant physics designed to be close to the correct mass of the charm quark. The numerical work uses the tree-level improved Lüscher-Weisz gauge action in \(N_f=3+1\) Lattice QCD.

Speaker: Felix Stollenwerk (Humboldt University Berlin)

Slides lat14_stollenwerk.pdf

Theoretical Developments: Parallel 7E

Convener: Hidenori Fukaya (Osaka University)

307 Optimisation of Quantum Evolution Algorithms

A specific unitary evolution operator can be constructed in many different ways, corresponding to different Hamiltonian trajectories between the desired end-points. An optimal trajectory can then be selected to make the evolution have the best computational complexity and control over errors. Using Grover's quantum search algorithm as an explicit example, it is shown that the complexity has a power-law dependence on error when a straightforward Lie-Trotter formula is used, and it becomes logarithmic in error when reflection operators are used. The exponential change in error control is surprising, and can be used to improve importance sampling methods. The key concept is to make the evolution steps as large as possible while obeying the constraints of the problem. In particular, we can understand why overrelaxation algorithms are superior to small step size algorithms.

Speaker: Prof. Apoorva Patel (Indian Institute of Science, Bangalore, India)

Slides qhamsim.pdf

308 Tensor renormalization group study of the 2d O(3) model

We study the two-dimensional O(3) model on the lattice using the Tensor Renormalization Group (TRG) approach, with the goal of understanding asymptotic scaling at both the large volume, and large beta limit. Harmonic analysis on the Boltzmann weight introduces a sign problem into the partition function, which makes the model difficult to study with the Worm Algorithm. The TRG is insensitive to the sign problem because it relies on projections onto eigenstates of positive matrices. Thermodynamic quantities are calculated for finite volumes, as well as the infinite volume limit, and compare well with Monte Carlo results. Prospects of parallelizing the TRG method to enable large scale calculations, which would aid in the computation of correlation functions, are briefly discussed, along with our progress on implementing these algorithms on the Blue Gene/Q.

Speaker: Judah Unmuth-Yockey (University of Iowa)

Slides judahlat2014.pdf

309 Energy-momentum tensor on the lattice and Wilson flow

The energy-momentum tensor in lattice gauge theories requires renormalization because of the breaking of Poincare' group. The Wilson flow can be used in principle to set up non-perturbative, well-defined and, possibly, practically convenient strategies to define a properly renormalized energy momentum tensor. I will present some preliminary data in this direction.

Speaker: Dr Agostino Patella (CERN and Plymouth University)

Slides patella.pdf

310 String tension from smearing and Wilson flow methods

Last year, we proposed a new method to extract string tension using 4-dimensional smearing method (PL B718 (2013) 1524). In this talk we first show that results using smearing method are equivalent to those obtained by Wilson flow once the time step \epsilon is sufficiently small. We then demonstrate the practical advantage of our method by applying it to the calculation of Creutz ratio in SU(3) Yang-Mills theory.

Speaker: Prof. Masanori Okawa (Hiroshima University)

Slides okawa.pdf

311 Tree level improvement of the gradient flow

The Yang-Mills gradient flow is considered in lattice perturbation theory at leading order of the gauge coupling and O(a^8) in the lattice spacing. Improved actions are incorporated for the gauge action, the flow itself and the observable for E(t). The results lead to a setup with O(a^6) improvement at tree level.

Speaker: Dr Daniel Nogradi (Eotvos University)

Slides ymflowimp.pdf

312 How to reduce O(a^2) effects in gradient flow observables?

The gradient flow has become a very useful tool both for scale setting and for defining suitable finite volume schemes for the gauge coupling. However, surprisingly large cutoff effects have been observed in some cases. We here investigate these effects at leading order in perturbation theory and reproduce qualitative features that have previously been observed in the context of scale setting. We demonstrate that the leading O(a^2) effects can be completely eliminated through a combined improvement of the observables, the action and the gradient flow. We then focus on finite volume couplings with SF boundary conditions and analyze the size of remaining cutoff effects, both from the bulk and the boundaries. This leads us to the definition of our preferred set-up and preliminary simulation results in the pure SU(3) gauge theory corroborate our findings.

Speaker: Stefan Sint (Trinity College Dublin & NIC@DESY-Zeuthen)

Slides sint_lat14.pdf sint_lat14.pdf

313 Locally smeared operator product expansions

We propose a new ``smeared'' operator product expansion (sOPE) in which the set of local operators in the OPE are replaced by their locally smeared counterparts, generated by the gradient flow. The flow time, or smearing, parameter serves as a regulator for both Wilson coefficients and operator products. Matrix elements determined nonperturbatively on the lattice using smeared degrees of freedom remain finite in the continuum limit, provided the physical smearing scale is kept fixed. We study the sOPE in scalar field theory and discuss the application to Deep Inelastic Scattering.

Speaker: Dr Christopher Monahan (College of William and Mary)

Slides cjmonahan_sOPE.pdf

Vacuum Structure and Confinement: Parallel 7F

Convener: Prof. Michael Ogilvie (Washington University)

314 The dynamical QCD string

Using the overlap Dirac operator we remove its lowest-lying eigenmodes from the valence quark propagators and study evolution of the J=1 meson masses. At the truncation energy about 50 MeV we observe a degeneracy of all possible U(2)_L * U(2)_R multiplets, i.e. the observed quantum levels have a symmetry larger than U(2)_L * U(2)_R and their energy does not depend on the spin orientation of quarks and their parities. We interpret these energy levels as the quantum levels of a dynamical QCD string that connects the ultrarelativistic quark and antiquark.

Speaker: Prof. Leonid Glozman Glozman (University of Graz)

Slides xqcd2014_neu.pdf

315 Study of axial magnetic effect

The axial magnetic field, which couples to left- and right-handed fermions with opposite signs, may generate an equilibrium dissipationless energy flow of fermions in the direction of the field even in the presence of interactions. In this report numerical observation of the Axial Magnetic Effect in SU(2) lattice gauge theory is presented. The temperature behavior of the Axial Magnetic Effect is studied. It is shown that in the confinement (hadron) phase the effect is absent. In the deconfinement transition region the conductivity quickly increases, reaching the asymptotic T^2 behavior in a deep deconfinement (quark-gluon plasma) phase.

Speaker: Mr Victor Braguta (IHEP)

Slides braguta.pdf

316 Surface operators study within the lattice QCD

The most important probes for the phase states of a four-dimensional gauge field theory are the Wilson and t'Hooft line operatros that are defined on one-dimensional curves in the space-time. However, for more detail understanding of four-dimensional gauge field theory dynamics and vacuum topology we need additional probes expressed by operators defined on the subspaces with higher dimensions. Possible candidates are operators that are defined on the two-dimensional surface in the four-dimensional space-time. In the present work the surface operator in the lattice QCD is studied. The Witten parameter dependence on the surface area and volume studied in confinement and deconfinement phases.

Speaker: Dr Alexander Molochkov (Far Eastern Federal University)

Slides Molochkov_Lattice_2014.pdf

317 Screening without dynamical quarks

Screening of external charges by electric fluxes induced by periodic boundary conditions in two dimensional gauge theories will be discussed. Subsequently, the less known problem of introducing sources with arbitrary charge, i.e. non-congruent with an elementary one, will be presented and elaborated. Finally the new, classical continuum limit of lattice formulation will be proposed and shown to reproduce confining potential with an arbitrary classical charge. Connection with the massive Schwinger model will be also indicated.

Speaker: Prof. Jacek Wosiek (Jagellonian University)

Slides v2.pdf

318 two-dimensional phase structure of SU(2) gauge-Higgs model

We study numerically the phase structure in two dimensions with SU(2) gauge-Higgs coupling. We calculate the static potential from Wilson Loop, W propagator and the order parameter related to a transition between the confinement-like phase and Higgs-like phase. Our results suggest that there is a confinement-like phase and Higgs-like phase, even in two dimensions. In the confinement-like phase, the static potential rises linearly with string breaking at large distances, while in the Higgs-like phase, it is of Yukawa type, consistent with a Higgs-type mechanism. The correlation length obtained from the W propagator has a maximum between these phase.

Speaker: Mr Shinya Gongyo (Kyoto University)

Slides Lattice2014(2014.06.26)_ver2.pdf

319 van Baal's legacy: From renormalons to bions

This talk presents a summary of our current understanding of confinement problem in non-abelian gauge theories. It is dedicated to the memory of Pierre van Baal, who contributed to the field significantly. I will review recent semi-classically calculable realization of confinement in various gauge theories. In particular, I will describe the role of monopole-instantons(realized by van Baal), and their role in neutral and magnetic bions, and the relation of these semi-classical saddles to 't Hooft's elusive renormalon problem. The techniques I describe uses resurgence theory, and related Lefschetz thimble (homology cycle) decomposition of path integrals.

Speaker: Mithat Unsal (North Carolina State University)

Slides Pierre-Resurgence-bion.pdf

Friday, 27 June

Plenary

Convener: Prof. Hartmut Wittig (University of Mainz)

320 Hadron Spectroscopy

Speaker: Prof. Sasa Prelovsek (University of Ljubljana)

Slides prelovsek_lat14.pdf

321 New algorithms for finite density QCD

Speaker: Dr Denes Sexty (Institut für Theoretische Physik, Universität Heidelberg)

Slides sexty_lattice2014.pdf

322 Wilson flow and renormalization

Speaker: Dr Alberto Ramos (NIC @ DESY, Zeuthen)

Slides ramos.pdf

10:45 Coffee Break

Plenary

Convener: Prof. Stephen Sharpe (University of Washington)

323 Wilson Award

Slides endrodi_lat14.pdf wilson_award_lat14.pdf

324 Hidden exact symmetry in graphene

The emergence of massless Dirac fermion in graphene has attracted attention in recent years due to the remarkable features. The tight-binding honeycomb lattice hamiltonian to explain this feature has a close analogy with "the staggered fermion" which is widely used in lattice gauge theory. Employing the position space formalism developed in lattice gauge theory, we reformulate the tight-binding honeycomb model. We show that there exists a hidden exact symmetry at finite lattice spacing, which protects the masslessness of the Dirac fermion.

Speaker: Prof. Tetsuya Onogi (Osaka University)

Slides slide_onogi4.pptx

Algorithms and Machines: Parallel 8F

Convener: Prof. Steve Gottlieb (Indiana University)

325 An algorithm for thimble regularization of lattice field theories (and possibly not only for that)

In the context of thimble regularization of lattice field theories we are developing a new simulation algorithm. The main difficulty is to devise a sampling of configurations on a non-trivial manifold, which is defined as the hypersurface formed by the union of all paths of steepest descent of the complex action ending in a given saddle point. The main point with the new algorithm is the one-to-one correspondence of configurations and action values on a given steepest descent curve, which can in turn be seen as a steepest ascent if one changes the sign of the "time" variable. We discuss the possible extensions of the algorithm to more general field theories. In the context of Lattice QCD the possible main advantage could be a mitigation of the problems connected to different topological sectors.

Speaker: Dr Francesco Di Renzo (University of Parma and INFN)

Slides fdr_LAT2014.pdf

326 A Method to Calculate Conserved Currents and Fermionic Force for the Lanczos Approximation to the Overlap Dirac Operator

The overlap Dirac operator at finite chemical potential can be efficiently computed with the two-sided Lanczos algorithm. Compared with other methods the Lanczos algorithm has the advantage that it takes into account information about the source vector when constructing an approximation to the overlap operator. In order to study transport coefficients in terms of correlators of conserved currents or to calculate the fermionic force in Hybrid Monte-Carlo simulations with the Lanczos approximation to overlap, one needs to calculate the derivative of this approximate overlap operator over the gauge field. We found that a straightforward algorithmic differentiation approach leads to huge numerical errors and is not feasible even for small lattice sizes. In this talk we argue that it is possible to simultaneously compute the action of the overlap operator and its derivative on a source vector. Using a matrix function identity, found by R. Mathias, we show that the calculation can be done without knowledge of the derivative of the Lanczos algorithm. To this end one has to apply the Lanczos algorithm to a block Toeplitz matrix of some special form, which acts on the linear space with two times larger dimension than the dimension of the original overlap operator. We present preliminary results and show that our method is numerically stable.

Speaker: Mr Matthias Puhr (University Regensburg)

Slides talk.pdf

327 Conjugate Directions in Landau and Coulomb Lattice Gauge Fixing

We provide details of our implementation of a non-linear conjugate gradient method for Landau and Coulomb gauge fixing with Fourier acceleration. We find clear improvement over the Fourier accelerated steepest descent method, with the average time taken for our algorithm to converge to a fixed, high accuracy, being lower by a factor of 2 to 4 for several lattice volumes.

Speaker: Dr Renwick Hudspith (York University)

Slides RJH_lattice_2014.pdf

328 A filtering technique for the temporally reduced matrix of the Wilson fermion determinant

The Wilson fermion determinant can be written in the form of a series expansion in fugacity z=exp(mu/T), provided that the eigenmodes of the temporally reduced operator are obtained. Since the calculation of all eigenmodes rapidly becomes prohibitive for larger volumes, we develop a method to calculate only the low-energy eigenmodes of the reduced matrix using a matrix filetering technique. This provides a basis of an approximation to neglect uninteresting ultraviolet contributions.

Speaker: Dr Keitaro Nagata (KEK)

Slides Lattice2014_10.pdf

329 pyQCD: A Native Lattice Simulation Package for Python

I demonstrate pyQCD, a native Python library providing an extensible API for single-node lattice measurements and simulations. Boost.Python is used to wrap the underlying C++ code and expose an interface to Python for the generation of propagators and configurations, both of which are returned as numpy ndarray types. The library can take advantage of GPU technology by using CUDA where possible to accelerate Dirac operator inversions. The package provides a set of tools for rapid prototyping and testing of algorithms or lattice measurements prior to their implementation in production code.

Speaker: Mr Matthew Spraggs (University of Southampton)

Slides http://nbviewer.ipython.org/github/mspraggs/Lattice2014/blob/master/Lattice%202014%20supplementary.ipynb

Application beyond QCD: Parallel 8G

Convener: Dr Eigo Shintani (Mainz University)

330 Solution to new sign problems with Hamiltonian Lattice Fermions

We present a solution to the sign problem in a class of particle-hole symmetric Hamiltonian lattice fermion models on bipartite lattices using the idea of fermion bags. The solution remains valid when the particle hole symmetry is broken through a staggered chemical potential term. This solution allows, for the first time, simulations of some massless four-fermion models with minimal fermion doubling and with an odd number of fermion flavors using ultra-local actions. One can thus study a variety of quantum phase transitions that have remained unexplored so far due to sign problems.

Speaker: Ms Emilie Huffman (Duke University)

Slides Lattice2014Talk-6-27-2014.pdf

331 Glueball masses in 2+1 dimensional SU(N) gauge theories with twisted b.c.

We analyze 2+1 dimensional Yang-Mills theory regularized on a lattice with twisted boundary conditions in the spatial directions. In previous work it was shown that the observables in the non-zero electric flux sectors obey the so-called x-scaling, i.e. depend only on the variable x~NL/b and the magnetic flux, given by the parameters of the twist (L being the length of the spatial torus and b the inverse 't Hooft coupling). It is conjectured that this scaling is obeyed by all physical quantities. In this work we extend the previous analyses to the zero-flux (glueball) sector. We study the x-scaling conjecture in this sector from the perturbative small-volume regime to the non-perturbative one.

Speaker: Dr Mateusz Koren (IFT UAM-CSIC Madrid)

Slides koren_glueball.pdf

332 Spectrum and Observables in Yang-Mills-Higgs Theory

The Higgs sector of the standard model, the Higgs and the W/Z bosons, is a quite peculiar theory. Because of the Higgs effect, in some cases the observable particles, i.e. gauge-invariant bound states, have the same mass as the elementary particles. This is what makes perturbation theory in the electroweak sector possible. Under which condition this holds true is not only important for understanding the Higgs sector itself, but may have severe implications for observable states in generic higgsed theories. The spectrum of observables and elementary particles, and thus the validity of a perturbative picture, is studied in a large area of the phase diagram of Yang-Mills-Higgs theory, starting from the QCD-like domain into the region of a potentially heavy Higgs. The results show that the low-lying spectrum depends on whether the theory is in a QCD-like region or a Higgs-like region, but the spectrum is otherwise rather inert to the microscopic details for a wide range of parameters. The applicability of a simple perturbative description is found to be restricted to only an intermediate range of 'Higgs' masses.

Speaker: Dr Axel Maas (University of Jena)

Slides lattice14.pdf

333 Spontaneous chiral symmetry breaking and chiral magnetic effect in Weyl semimetals

We study interacting Dirac fermions with chiral imbalance (modelled by a chiral chemical potential) in the mean-field approximation and find that the chiral imbalance is strongly enhanced due to spontaneous chiral symmetry breaking. We then consider the Chiral Magnetic Effect (CME) in the linear response approximation and find that in a phase with broken chiral symmetry the CME current is saturated by vector mesons with different polarizations, which are mixed in chirally imbalanced matter. It turns out that strong screening of CME current in this phase is exactly compensated by enhancement of chiral imbalance, so that the chiral magnetic conductivity remains finite in the strong-coupling limit. We illustrate these conclusions for a Weyl semimetal which is modelled by a single flavour of Wilson-Dirac fermions with chiral chemical potential. We also argue that this model is free of the sign problem by virtue of time-reversal symmetry and can be efficiently simulated using the Rational Hybrid Monte-Carlo algorithm.

Speaker: Dr Pavel Buividovich (Regensburg University)

Slides cme_and_schsb_lattice2014.pdf

334 The electro weak transition and the equation of state in the SU(2)-Higgs-model

Since the discovery of the Higgs particle at the LHC it is possible to investigate the equation of state for the electro weak transition in the SU(2)-Higgs-model at physical parameters. We will present a line of constant physics and preliminary results on the equation of state for small Nt values. The data was obtained by simulation with a combined heatbath and overrelaxation algorithm.

Speaker: Ms Jana Günther (Bergische Universität Wuppertal)

Slides Vortrag.pdf

Hadron Structure: Parallel 8D

Convener: Kim Maltman

335 Towards the physical point hadronic vacuum polarisation from Möbius DWF

We present steps towards the computation of the leading-order hadronic contribution to the muon anomalous magnetic moment on RBC/UKQCD physical point DWF ensembles. We discuss several methods for controlling and reducing uncertainties associated to the determination of the HVP form factor.

Speaker: Marina Marinkovic (University of Southampton)

Slides marinkovic_lat14.pdf

336 Leading-order hadronic contribution to $g_\mu-2$ from $N_f=2+1$ simulations down to the physical pion mass

For the Budapest-Marseille-Wuppertal collaboration. We present preliminary lattice QCD results for the leading-order hadronic contribution to the muon anomalous magnetic moment. Computations are based on 2+1 flavour simulations with HEX-smeared clover fermions and pion masses down to its physical value. Besides the traditional approach, several methods implementing derivatives of the hadronic vacuum polarization are investigated and compared.

Speaker: Mr Rehan MALAK (Mr)

Slides RehanMalakLattice2014.pdf

337 A Study of the anomalous magnetic moment of the muon computed from the Adler function

We compute the Adler function from vacuum polarization data with twisted boundary conditions using numerical derivatives. The study is based on CLS ensembles with two flavours of O(a) improved Wilson fermions. To describe the momentum dependence and to extrapolate the lattice data to the continuum limit and to the physical point, we perform a combined fit and compare our results for the Adler function to phenomenology. In addition, the Adler function provides an alternative method to compute the anomalous magnetic moment of the muon. We compare our results from this approach to a determination using a more standard method.

Speaker: Mr Hanno Horch (University of Mainz)

Slides HannoHorch_Lattice2014.pdf

338 Study of the couplings of QED and QCD from the Adler function

The QCD contributions to the vacuum polarisation function are responsible for a large fraction of the theoretical uncertainty in the running of the QED coupling and therefore limit its impact on electroweak precision tests. We use lattice simulations with N_f=2 O(a) improved Wilson fermions to determine the Adler function in a broad range of momentum transfer Q^2. The running of the QED coupling, including valence contributions from u, d, s and c quarks, is compared to phenomenological results at intermediate Q^2 values. In the large Q^2 regime, the lattice determination of the Adler function is fitted to perturbation theory in order to explore the feasibility of a determination of the strong coupling constant.

Speaker: Gregorio Herdoiza (KPH Mainz and IFT Madrid)

Slides talk.pdf

339 Towards the large volume limit - An application to hadronic contributions to muon g-2 and EM corrections

We explore ways to decrease parts of the finite volume error and apply the method to the hadronic contributions to muon g-2.

Speaker: Christoph Lehner (BNL)

Slides talk-v2.pdf

Hadron spectroscopy and interaction: Parallel 8B

Convener: Prof. Colin Morningstar (Carnegie Mellon University)

340 Electromagnetic mass splittings from dynamical lattice QCD+QED

First results on electromagnetic mass splittings of octet mesons and baryons from a fully dynamical simulation of QCD+QED are presented.

Speaker: Prof. Gerrit Schierholz (DESY)

Slides lat14.pdf (Protected)

341 Finite volume effects and the electromagnetic contributions to kaon and pion masses

We report on the MILC Collaboration calculation of electromagnetic effects on light pseudoscalar mesons. The simulations employ asqtad staggered dynamical quarks in QCD plus quenched photons, with lattice spacings varying from 0.12 to 0.06 fm. Finite volume corrections for the MILC realization of lattice electrodynamics have been calculated in chiral perturbation theory theory and applied to the lattice data. These corrections differ from those calculated by Hayakawa and Uno because our treatment of zero modes differs from theirs. Updated results for the corrections to "Dashen's theorem" are presented.

Speaker: Prof. Claude Bernard (Washington University St. Louis)

Slides lat14_EM.pdf

342 Search for Z_c(3900) on the lattice with twisted mass fermions

Recently a charged resonance-like structure $Z_c(3900)$ has been observed in several experiments. The invariant mass of this structure is close to the DD* threshold, and one possible interpretation is a molecular bound state formed by the D and $\bar{D}*$ mesons. We study the low-energy scattering of $D\bar{D}^*$ using lattice QCD with N_f = 2 twisted mass fermion configurations with three pion mass values. The threshold scattering parameters, namely the scattering length a_0 and effective range r_0, for the s-wave scattering in $J^P = 1^+$ channel are extracted. Our results indicate that the interaction of this channel is weakly repulsive. To further investigate the properties of $Z_c(3900)$, we redo the calculation with some improvements. We employ the stochastic LapH smearing method, which greatly improves the precision of our results. We also enlarge the operator basis and study the coupled channel effects.

Speaker: Liuming Liu (University of Bonn)

Slides talk_Liu.pdf

343 Evidence for the charged charmonium-like state Zc+ from lattice QCD

We perform a lattice QCD simulation of the charmonium-like channel, where experiments recently found several manifestly exotic states named Zc+ with flavor content bar c c bar d u. In addition to identifying all the scattering states we also observe an additional level in the simulation, which we attribute to Zc+.

Speaker: Mr Luka Leskovec (Institute Jozef Stefan)

Slides leskovec_lattice2014.pdf

344 Updated results from maximally twisted mass QCD at the physical point

In this contribution, updated results from simulations by the European Twisted Mass Collaboration at the physical point using Wilson twisted mass fermions with a clover term are presented. We discuss results for the pseudoscalar decay constants $f_K$, $f_D$ and $f_{D_s}$ and the corresponding masses. In addition, we provide evidence for a largely reduced flavour symmetry breaking in the presence of a clover term.

Speaker: Mr Bartosz Kostrzewa (Humboldt Universität zu Berlin, Institut für Physik, Newstonstr. 15, 12489 Berlin, Germany / NIC, DESY, Zeuthen, Platanenallee 6, D-15738 Zeuthen, Germany)

Slides kostrzewa_lattice_2014.pdf

Nonzero temperature and Density: Parallel 8A

Convener: Tereza Mendes

345 Deconfining temperatures in SO(N) and SU(N) gauge theories

We present our current results for the deconfining temperatures in SO(N) gauge theories in 2+1 dimensions. SO(2N) theories may help us to understand QCD at finite chemical potential since there is a large-N orbifold equivalence between SO(2N) QCD-like theories and SU(N) QCD and SO(2N) theories do not have the sign problem present in QCD. We show that the deconfining temperatures in these two theories match at the large-N limit. We also present results for SO(2N+1) gauge theories and compare results for SO(6) with SU(4) gauge theories, which have the same Lie algebras but different centres.

Speaker: Richard Lau (University of Oxford)

Slides lattice2014.pdf

346 The density of states from first principles

We present a novel algorithm to compute the density of states, which is proven to converge to the correct result. The algorithm is very general and can be applied to a wide range of models, in the frameworks of statistical mechanics and lattice gauge theory. All the thermal or quantum expectation values can then be obtained by a simple integration of the density of states. As an application, a numerical study of 4d U(1) compact lattice gauge theory is presented.

Speaker: Dr Roberto Pellegrini (College of Science, Swansea University, Swansea, SA2 8PP, UK)

Slides density.pdf

347 A novel density of state method for complex action system

Recently, a new and efficient algorithm (the LLR method) has been proposed for computing density of states in statistical systems and gauge theories. In this talk, we explore whether this novel density of state method can be applied to numerical computations of observables in systems for which the action is complex. To this purpose, we introduce a generalised density of states, in terms of which integrals of oscillating observables can be determined semi-analytically, and we define a strategy to compute it with the LLR method. As a case study, we apply these ideas to the Z(3) spin model at finite density, finding a remarkable agreement of our results for the phase factor with those obtained with the worm algorithm for all explored chemical potentials, including values for which there are cancellations over sixteen orders of magnitudes. These findings open new perspectives for dealing with the sign problem on physically more relevant systems.

Speaker: Prof. Lucini Biagio (Swansea University)

Slides lucini_lat14.pdf

348 Quark number susceptibilities from fugacity expansion at finite chemical potential

Generalized quark number susceptibilities have been proposed to be good probes for the phase transition in QCD and in the search of a critical point. In this work we explore the possibilities of the expansion in the fugacity parameter $e^{\mu\beta}$ which has features which make, in particular, quark number related bulk observables easily accessible. We will present results at finite chemical potential up to the 4th order of generalized susceptibilities, its ratios and comparisons to model calculations.

Speaker: Hans-Peter Schadler (University of Graz)

Slides 2014_laittce2014_schadler_fugacity_final_20140626.pdf

349 Shear Viscosity from Lattice QCD

This talk is on recent efforts to determine the shear viscosity $\eta$ in the deconfined phase from lattice QCD. The main focus is on the integration of the Wilson flow in the analysis to get a better handle on the infrared behaviour of the spectral function which is relevant for transport. Also the non-perturbative renormalization strategy applied for the energy momentum tensor is discussed. At the end some quenched results for temperatures up to $4.5T_c$ are presented.

Speaker: Mr Simon Mages (University of Regensburg)

Slides Excitation

Physics beyond the standard model: Parallel 8C

Convener: Anna Hasenfratz

350 Nuclear physics beyond QCD

We consider QCD-like, composite models of dark matter and investigate what role nuclear physics may play in the dark sector. We compute the multi-particle spectrum of SU(N_c=2) gauge theory with two fundamental fermions, finding strong evidence for the existence of bound multi-hadron systems (nuclei) in this theory. We briefly discuss the rich phenomenological consequences of such strong interaction dynamics.

Speaker: Dr William Detmold (MIT)

Slides Lattice2014.pdf

351 The bosonic side of composite dark matter

One intriguing coincidence in cosmology is that the observed dark matter and baryonic densities are within a factor of 5 in magnitude. A natural explanation for such a coincidence is that the origin of the dark matter density is intimately related to the early universe processes that led to the baryon asymmetry. Many of these “asymmetric” dark matter scenarios favor a strongly coupled composite sector ala QCD, where neutral, long-lived composites can survive to be observed today, but still have charged constituents to interact with early universe baryogenesis. As a result, these neutral composites are expected to interact with ordinary matter through Higgs exchange or higher dimensional electromagnetic interactions such as magnetic moments, charge radii, and polarizabilties; the last of which cannot be avoided and can provide a lower bound for these theories. In this talk, I will discuss a theory of bosonic baryons in SU(4) gauge theory that only interact via Higgs exchange and polarizabilities. In particular, I will focus on the spectrum and Higgs exchange properties, whose interaction strength can vary based on ratios of the chiral to vector-like mass couplings. These calculations provide the foundation for future calculations of polarizabilities, which will ultimately bound this class of composite dark matter.

Speaker: Dr Michael Buchoff (Institute for Nuclear Theory)

Slides Buchoff_Lattice_2014.pdf

352 Dark matter baryon candidates in the sextet gauge model

The strongly coupled near-conformal gauge theory with two fermion flavors in the two index symmetric (sextet) representation of the SU(3) color gauge group is the minimal realization of the composite Higgs mechanism. We discuss the baryon mass spectrum in this theory using staggered fermion operators to identify dark matter candidates.

Speaker: Dr Santanu Mondal (Eotvos University, Institute for Theoretical Physics, Budapest 1117, Hungary)

Slides talk.pdf

353 Scattering lengths in SU(2) Gauge Theory with two Fundamental Fermions

We investigate non perturbatively scattering properties of Goldstone Bosons in SU(2) gauge theory with two Wilson fermions in the fundamental representation. Such a theory can be used to build extensions of the Standard Model that unifies Technicolor and pseudo Goldstone composite Higgs models. The leading order contribution to the scattering amplitude of Goldstone bosons at low energy is given by the scattering lengths. In the context of technicolor extensions of the Standard Model the scattering lengths are constrained by WW scattering measurements. We first describe our setup and in particular the expected chiral symmetry breaking pattern. We then discuss how to compute them on a lattice and give preliminary results using finite size methods.

Speaker: Dr Vincent Drach (CP3 Origins &amp;amp; DIAS)

Slides lat2014_drach.pdf

354 Gauge-invariant signature of spontaneous gauge symmetry breaking by the Hosotani mechanism

We study the Hosotani mechanism on the lattice and show with the use of gauge invariant observables that SU(3) can break either to SU(2)xU(1) or U(1)xU(1). The novelty in this study is the strict gauge invariance of the observables used. We take advantage of the inability of a U(1) flux to decay in the continuum limit. One interesting consequence is that the SU(2) and U(1) subgroups rotate locally in representations space but the introduced flux always follows the U(1) subgroup. We also investigate the stability of U(1) monopoles when the gauge symmetry is broken.

Speaker: Philippe de Forcrand (ETH Zurich)

Slides U1_LAT14.pdf

Theoretical Developments: Parallel 8E

Convener: Prof. Ulli Wolff (Humboldt University, Berlin)

355 A construction of the Schrodinger Functional for Möbius Domain Wall Fermions

We investigate the universality of Möbius Domain Wall Fermions (MDWF) in the Schrödinger Functional (SF) scheme at tree level. We introduce the SF boundary condition to the MDWFs by adding a temporal boundary operator. When the fifth dimensional parameters of the MDWF are a constant, this construction seems to be natural according to the Luescher’s universality prescription for the overlap fermion and Takeda’s construction for the standard domain wall fermion (DWF). We observe that the four dimensional effective operator derived from this DWF approaches to the continuum operator with the SF boundary condition at tree level. In order to construct the SF boundary condition for the Optimal DWFs, the fifth dimensional parameters depend on the fifth lattice index, we must impose the fifth dimensional parity symmetry on the parameters so as to maintain both the discrete symmetries and the chiral symmetry breaking property of the SF boundary term. This additional symmetry makes the MDWF with the SF boundary condition impossible to introduce Zolotarev optimal coefficients. We will discuss how to realize the optimal type of the MDWF with the SF boundary condition.

Speaker: Ms Yuko Murakami (Hiroshima University)

Slides lattice2014_v14.pdf

356 Crank-Nicolson discretization scheme and lattice fermions

It is well known that Crank-Nicolson discretization scheme is second order accurate in time. Its application in the case of the Dirac operator leads to a lattice theory with reduced doublers and broken parity. Adding a 3-space Wilson term one obtains a single fermion which is second order accurate in time. In the case of an imaginary term the doubler degeneracy is lifted and the ground state describes a single Weyl fermion.

Speaker: Prof. Artan Borici (Uiversity of Tirana)

Slides ArtanBorici.pdf

357 Fermion Mass Generation without a chiral condensate

Massless fermions can become massive due to interactions through the mechanism of Spontaneous Symmetry Breaking (SSB). This mode of mass generation is popular and has been used in the Standard Model. Here, we explore the possibility of fermions acquiring a mass through interactions, but without SSB.\\ We consider a fermion system on a cubical lattice and introduce an on-site four-fermion interaction with coupling constant $U$. Using the symmetries of the system on the lattice, we can predict the existence of massless fermions for small $ U $. For very large values of $ U $, we can argue that the fermions become massive without the formation of a fermion bilinear condensate. Monte Carlo results suggest that chiral condensate is zero for all values of the coupling constant. We show that the phase transition from the massless to the massive phase is second order. We also calculate the critical exponents of the theory. The existence of a second order phase transition implies that one can take the continuum limit of the lattice model and obtain an interesting Quantum Field Theory with a new mechanism for fermion mass generation.

Speaker: Mr Venkitesh Ayyar (Duke University)

Slides Ayyar_ppt.pdf Ayyar_ppt.pptx

358 The Hadronic Spectrum and Confined Phase in (1+1)-Dimensional Massive Yang-Mills Theory

Massive Yang-Mills theory is known to be renormalizable in 1+1 dimensions. The gluon mass is introduced by coupling the gauge field to an SU(N) principal chiral nonlinear sigma model. The proof of renormalizability relies on the asymptotic freedom of the sigma model. However, renormalization forces the gluon mass to infinity. The continuum theory is in a confined phase rather than a Higgs phase. The physical excitations of the system are hadron-like bound states of sigma model particles. We calculate the massive spectrum of meson-like bound states analytically, using the exact S-matrix of the sigma model. The baryon-like spectrum can be found in principle by solving a quantum mechanical N-body problem. We remark on the evidence for the confined phase found for SU(2) in recent lattice simulations by Gongyo and Zwanziger. Their simulations show evidence for a Higgs-like phase which seems to disappear with increasing volume, finding agreement with our analysis in the continuum.

Speaker: Dr Axel Cortes Cubero (City University of New York)

Slides Lattice2014Cubero.pdf

15:55 Coffee Break

Hadron Structure: Parallel 9D

Convener: Rajan Gupta

359 A Feynman-Hellmann approach to the spin structure of hadrons

By introducing an external spin operator to the fermion action, the quark-line connected matrix elements relevant for quark spin fractions of hadrons are extracted from the linear response of the hadron energies using the Feynman-Hellmann (FH) theorem. At the SU(3)-flavour symmetry point, we find that the connected quark spin fractions are universally in the range 55-70% for vector mesons and octet and decuplet baryons. There is an indication that the amount of spin suppression is quite sensitive to the strength of SU(3) breaking. Finally, I also hope to present preliminary results applying the FH technique to calculations of quark line disconnected contributions to hadronic matrix elements.

Speaker: Dr James Zanotti (University of Adelaide)

Slides Zanotti.pdf

360 Glue Helicity $\Delta G$ In the Nucleon

We present a lattice QCD calculation of the glue helicity $\Delta G$ in the nucleon for the first time. It is recently shown that the first moment of the glue helicity distribution can be obtained through the product of the the electric field $\vec{E}$ and the gauge field in the Coulomb gauge $\vec{A}_C$, i.e. $\vec{E} \times \vec{A}_C$ in the infinite momentum frame. We used the gauge field tensor from the overlap Dirac operator to check the frame dependence with several momenta. The calculation is carried out with valence overlap fermion on 2+1 flavor DWF gauge configurations on the $24^3 \times 64$ lattice with the light sea quark mass corresponds to a pion mass of 330 MeV.

Speaker: Raza Sufian (University of kentucky)

Slides GlueHelicityRaza.pdf

361 Nucleon transverse momentum-dependent parton distributions from domain wall fermion calculations at 297 MeV pion mass

Lattice QCD calculations of transverse momentum-dependent parton distributions (TMDs) in a nucleon are performed based on a definition of TMDs via hadronic matrix elements of quark bilocal operators containing staple-shaped gauge connections. A parametrization of the matrix elements in terms of invariant amplitudes serves to cast them in the Lorentz frame preferred for the lattice calculation. Using a RBC/UKQCD domain wall fermion ensemble corresponding to a pion mass of 297 MeV, on a lattice with spacing 0.084 fm, selected TMD observables are accessed and compared to previous explorations at heavier pion masses on coarser lattices.

Speaker: Michael Engelhardt (New Mexico State University)

Slides Engelhardt_Lattice2014.pdf

362 Nonperturbative renormalisation for low moments of light-meson distribution amplitudes

We discuss nonperturbative renormalisation of the leading-twist flavour non-singlet operators needed for the calculation of the first and second moments of light-meson distribution amplitudes. On the lattice we use a regularisation-independent symmetric (or non-exceptional) momentum scheme, RI/SMOM, which, for the second moment, allows us to include mixing with a total-derivative operator. We calculate the conversion functions needed to connect the RI/SMOM results to MSbar.

Speaker: Jonathan Flynn (University of Southampton)

Slides jmf_latt14_hs9d.pdf

363 A framework for the calculation of the $\Delta N\gamma^*$ transition form factor on the lattice

Using the non-relativistic effective field theory framework in a finite volume, we discuss the extraction of the $\Delta N\gamma^*$ transition form factors from lattice data. A counterpart of the L\"uscher approach for the matrix elements of unstable states is formulated. In particular, we thoroughly discuss various kinematic settings, which are used in the calculation of the above matrix element on the lattice. The emerging L\"uscher-Lellouch factor and the analytic continuation of the matrix elements into the complex plane are also considered in detail. A full group-theoretical analysis of the problem is made, including the partial-wave mixing and projecting out the invariant form factors from data.

Speaker: Dr Akaki Rusetsky (HISKP, University of Bonn)

Slides LATTICE-2014.pdf

364 Signal/noise optimization strategies for stochastically estimated correlation functions

Numerical studies of quantum theories usually rely upon an accurate determination of stochastically estimated correlation functions in order to extract information about the spectrum of the theory and matrix elements of operators. The reliable determination of such correlators is often hampered by an exponential degradation of signal/noise at late time separations. I will demonstrate that it is sometimes possible to achieve significant enhancements of signal/noise by appropriately optimizing correlators with respect to the source and sink interpolating operators. The ideas will be demonstrated for both a toy model, and single hadron correlators in QCD.

Speaker: Michael G Endres (MIT)

Slides Lattice2014-Endres.pdf

Nonzero temperature and Density: Parallel 9A

Convener: Gergely Endrodi

365 Effective Polyakov line actions, and their solutions at finite chemical potential

I explain the “relative weights” strategy for deriving effective Polyakov line actions, at finite chemical potentials, from the underlying lattice gauge theories. Gauge-Higgs and heavy quark models are the examples considered. The effective Polyakov line theories still have a severe sign problem, and I compare results obtained using mean field and complex Langevin methods to solve such theories.

Speaker: Dr Jeff Greensite (San Francisco State University)

Slides Lat14a.pdf

366 Chiral dynamics in the low-temperature phase of QCD

We investigate the low-temperature phase of QCD and the crossover region with two light flavors of quarks. The chiral expansion around the point $(T, m_q = 0)$ in the temperature vs. quark-mass plane indicates that a sharp real-time excitation exists with the quantum numbers of the pion. We determine its dispersion relation and test the applicability of the chiral expansion. The time-dependent correlators are also analyzed using the Maximum Entropy Method (MEM), yielding consistent results. Finally, we test the predictions of ordinary chiral perturbation theory around the point $(T = 0, m_q = 0)$ for the temperature dependence of static observables. Around the crossover temperature, we find that all quantities considered depend only mildly on the quark mass in the considered range 8MeV $\leq \overline{m}^{\overline{\text{MS}} \leq$ 15MeV.

Speaker: Mr DANIEL ROBAINA (Institute of Nuclear Physics. Johannes Gutenberg University Mainz)

Slides RobainaPDR.pdf

367 Two-color QCD with chiral chemical potential

We present preliminary results of the study lattice SU(2) QCD phase diagram with chiral chemical potential. The simulation is carried out with dynamical staggered fermions without rooting. The dependences of the chiral density, Polyakov loop, chiral condensate and corresponding susceptibilities on the chiral chemical potential and temperature are measured.

Speaker: Mr Andrey Kotov (ITEP, Moscow)

Slides kotov_mu5.pdf

368 Deconfinement transition in two-flavour lattice QCD with dynamical overlap fermions in an external magnetic field

We study the influence of an external magnetic field on the deconfinement transition in two-flavour lattice QCD with physical quark charges. We use dynamical overlap fermions without any approximation such as fixed topology and perform simulations on a 16^3×6 lattice and at a pion mass around 500 MeV. The pion mass (as well as the lattice spacing) was determined in the independent runs on 12^3×24 lattices. We consider two temperatures, one of which is close to the deconfinement transition and the other is above it. Within our limited statistics the dependence of the Polyakov loop and chiral condensate on the magnetic field supports the "inverse magnetic catalysis" scenario in which the transition temperature decreases as the field strength grows.

Speaker: Mr Oleg Kochetkov (University of Regensburg)

Slides Kochetkov-lattice2014.pptx

369 Magnetic properties of the QCD medium

We present improved results regarding our determination of the magnetic susceptibility in QCD. We discuss also preliminary data on higher order terms contributions in B to the free energy and to the relative increase in the pressure.

Speaker: Mr Marco Mariti (University of Pisa & INFN)

Slides mariti.pdf

370 Effects of an external magnetic field on the QGP

We present results for the pressure of the quark-gluon plasma in the presence of a strong magnetic filed, calculated using a Taylor expansion in the field to 4th order. Our method does not require quantization of the magnetic filed and is computationally cheaper than calculations on ensembles generated with explicit magnetic fields.

Speaker: Ludmila Levkova (University of Utah)

Slides levkova_talk.pdf

Physics beyond the standard model: Parallel 9C

Convener: Simon Catterall

371 Last results of N=1 supersymmetric Yang-Mills theory with some topological insights

We summarize the last results of our collaboration concerning N=1 supersymmetric Yang-Mills theory in four dimensions on the lattice. We investigate the expected formation of supersymmetric multiplets of the lightest particles and the behaviour of the topological susceptibility approaching the supersymmetric and the continuum limit of the theory.

Speaker: Dr pietro giudice (University of Muenster)

Slides pietro_giudice_latt14.pdf

372 Non-renormalization theorem and cyclic Leibniz rule in lattice supersymmetry

We propose a lattice model of a complex SUSY quantum mechanics which realizes the non-renormalization theorem on lattice. In our lattice model, the Leibniz rule in the continuum, which cannot hold on lattice due to a no-go theorem, is replaced by the cyclic Leibniz rule (CLR) for difference operators. It is shown that the CLR allows two of four supercharges of the continuum theory to preserve while a naive lattice model can realize one supercharge at the most. A striking feature of our lattice model is that there are no quantum corrections to potential terms in any order of perturbation theory. This is one of characteristic properties of SUSY theory in the continuum. It turns out that the CLR plays a crucial role in the proof of the non-renormalization theorem. This result suggests that the CLR grasps an essence of supersymmetry on lattice.

Speaker: Prof. Makoto Sakamoto (Kobe University)

Slides sakamoto@Lattice2014.pdf

373 Spectrum of the SU(4) lattice gauge theory with fermions in the anti-symmetric two index representation

We study the SU(4) lattice gauge theory with Nf=2 Dirac fermions in the anti-symmetric two index (sextet) representation (the ``SU(4)/sextet" theory). This is a real fermion representation, which allows simulation at non-zero chemical potential with no sign problem. In addition, ``SU(4)/sextet'' is an interesting generalization of QCD, allowing direct exploration of an alternate large-N_c expansion with fermions in the sextet representation. In this talk, I will present our preliminary results on the baryon and meson spectrum of the theory and compare them with SU(3) results and large-N_c scaling.

Speaker: Dr Yuzhi Liu (University of Colorado, Boulder)

Slides Lattice2014_YL.pdf

374 Light composite scalar and other spectra in Nf=8 QCD

We (LatKMI Collaboration) present the first observation of a flavor-singlet scalar meson as light as the pion in Nf=8 QCD on the lattice, using the HISQ action. Such a light scalar meson can be regarded as a composite Higgs with mass 125 GeV, and may be a technidilaton, a pseudo Nambu-Goldstone boson of the approximate scale symmetry in walking technicolor. We also report the update about the chiral behavior of other spectra, particularly the pion and the rho meson masses, the pion decay constant and the chiral condensate, in order to test walking signals in Nf=8 QCD.

Speaker: Dr Kei-ichi Nagai (KMI, Nagoya University)

Slides lattice2014_nagai.pdf

375 Analysis of the scalar and vector channels in many flavor QCD

In the search for a composite Higgs boson in walking technicolor models, many flavor QCD is an attractive candidate. Particularly promising is the Nf=8 theory, which has been found to have a composite flavor-singlet scalar as light as the pion. Based on simulations of this theory with the HISQ action at various fermion masses in the LatKMI collaboration, we will present our preliminary results on the scalar decay constant using the fermionic bilinear operator. We will then discuss a possible relation between the scalar decay constant and the decay constant of the techni-dilaton, which would be identified with a composite Higgs boson. The (axial) vector current is used to compute the S-parameter and the vector meson decay constant. Chiral behavior of these low-energy quantities will be also discussed.

Speaker: Mr Hiroshi Ohki (Kobayashi-Maskawa Institute for the Origin of particles and the universe)

Slides Lattice2014_ohki.pdf

376 Phase structure and Higgs boson mass in a Higgs-Yukawa model with a dimension-6 operator

We investigate the impact of a $\lambda_6 \pi^6$ term included in a chiral invariant lattice Higgs-Yukawa model. Such a term could emerge from BSM physics at some larger energy scale. We map out the phase structure of the Higgs-Yukawa model with positive $\lambda_6$ and negative quartic self coupling. To this end, we evaluate the constraint effective potential in lattice perturbation theory and determine the magnetization of the model via numerical simulations which allow us to reach also non-perturbative values of the couplings. As a result, we find a complex phase structure with first and second order phase transitions identified through the magnetization. Further we analyze the effect of such a $\phi^6$ term on the Higgs boson mass to see, whether the standard model lower mass bound can be altered.

Speaker: Mr Attila Nagy (Humboldt University Berlin)

Slides Lattice_2014_nagy.pdf

Standard model parameters and renormalization: Parallel 9E

Convener: Prof. Gunnar Bali (University of Regensburg)

377 Using NSPT for the Removal of Hypercubic Lattice Artifacts

The quantification and subtraction of hypercubic lattice artifacts is essential for the calculation of non-perturbative renormalization constants. It has been shown that for the RI'-MOM scheme a large part of these artifacts can be calculated using Lattice Perturbation Theory (LPT), but these calculations are typically restricted to 1-loop order and to bilinear quark operators with one derivative at most. With Numerical Stochastic Perturbation Theory (NSPT) one may overcome this limitation and calculate hypercubic corrections beyond 1-loop order, for any operator and action. In this study, we explore the practicability of this approach and consider, as a first test, the case of Wilson fermion bilinear operators in a quenched theory.

Speaker: Mr Jakob Simeth (University of Regensburg)

378 An update on the status of NSPT computations

In recent years Numerical Stochastic Perturbation Theory (NSPT) has proven to be a viable tool to perform perturbative computation at high order on the lattice. Despite final results are equivalent to standard Feynman diagrams the approach is rather different and allows a numerical implementation similar to usual (nonperturbative) MonteCarlo. I will discuss final results for the computation of renormalization constants of quark bilinears for the regularizations defined by nf=2 Wilson fermions/tree level Symanzik improved gauge and nf=4 Wilson fermions/Iwasaki improved gauge. NSPT results will be compared with the ones coming from non perturbative determinations. I will also discuss current developments in the context of clover fermions.

Speaker: Dr Michele Brambilla (Università di Parma and INFN)

Slides brambilla_nspt_update.pdf

379 Calculating the glue helicity on the lattice with comments about renormalization

We discuss recent preliminary results for a lattice calculation of the glue helicity $\Delta_G$ in the Coulomb gauge. We have used the gauge field tensor defined from the overlap Dirac operator. The calculation is carried out with valence overlap quarks on 2+1 DWF gauge configurations on the $24^3 \times 64$ lattice which corresponds to a pion mass of 330 MeV. Finally, we discuss the perturbative renormalization matching of this operator to the continuum $\overline{MS}$ scheme at one-loop order in the Coulomb gauge.

Speaker: Dr Michael Glatzmaier (University of Kentucky)

Slides mglatzmaier-lattice-2014.pdf

380 Isospin Effects by Mass Reweighting

Most of today's lattice simulations are performed in the isospin symmetric limit in the light quark sector. A technique with moderate numerical cost to include effects of isospin breaking in the sea quark sector is mass reweighting. We will give a summary of the recent results on fine lattices with light quark masses. In general reweighting corrects the weight of an ensemble which is sampled by a specific algorithm. In the case of mass corrections the reweighting factor is a ratio of the fermion determinants. The evaluation of this factor for which we use stochastic methods and the factor itself introduce fluctuations which increase the statistical uncertainties. We will show the quark mass and volume dependence of these fluctuations in the case of isospin breaking. Towards the physical light quark masses the effect of the correction increases and can have a significant impact for precision measurements in the light quark sector.

Speaker: Mr Jacob Finkenrath (University of Wuppertal)

Slides lattice_talk_14.pdf

381 Renormalization of Flavor Singlet and Nonsinglet Fermion Bilinear Operators

We compute the difference in the renormalization of flavor singlet and nonsinglet fermion bilinear operators, to 2 loops in perturbation theory. Our results are applicable to a rather wide class of lattice actions with Symanzik improved gluons, stout links and clover fermions, including the Twisted Mass and SLiNC actions.

Speaker: Prof. Haralambos (Haris) Panagopoulos (Univeristy of Cyprus)

Slides Lattice2014_talk.pdf

Weak Decays and Matrix Elements: Parallel 9B

Convener: Oliver Witzel (Boston University)

382 $B\to\pi$ semileptonic form factors from unquenched lattice QCD

We update the lattice calculation of the $B\to\pi$ semileptonic form factors with a focus on the applications to the CKM matrix element $|V_{ub}|$. We use the MILC AsqTad 2+1-flavor lattice configurations at four lattice spacings and compute the matrix elements using the full-QCD valence quarks. We extrapolate the lattice data to continuum physics using the staggered chiral perturbation theory in the hard pion and SU(2) limit. We use a functional method to do the model-independent $z$ expansion of the lattice extrapolation which extends the result to the full kinematic range. To obtain $|V_{ub}|$, we simultaneously fit the most recent experimental measurements from BaBar and Belle with our lattice result. The updated value of $|V_{ub}|$ and its error budget are presented.

Speaker: Daping Du (Syracuse University)

Slides B2pi_lat14_Du.pdf

383 The B -> pi l nu and B_s -> K l nu form factors from 2+1 flavors of domain-wall fermions and relativistic b-quarks

We report results for the B→π and B_s→K semileptonic form factors using lattice QCD with domain-wall light quarks and relativistic b-quarks. We use the 2+1 flavor domain-wall Iwasaki gauge configurations generated by the RBC and UKQCD collaborations at two lattice spacings of a~0.08fm and a~0.11fm. Our lightest pion mass is about 290MeV. We perform the chiral and continuum extrapolations using hard-pion SU(2) chiral perturbation theory, and extrapolate the form factors to the full kinematic range using the model independent z-expansion. Finally, we fit the numerical lattice data for B -> pi simultaneously with the experimental measurements from BaBar and Belle to obtain the CKM matrix element |V_{ub}|.

Speaker: Dr Taichi Kawanai (Brookhaven National Laboratory)

Slides lattice2014_talk.pdf

384 Semileptonic form factors of pseudoscalar mesons from Nf=2+1+1 Twisted Mass lattice QCD

We present a lattice QCD determination of the vector and scalar form factors of the kaon semileptonic decay K->pi nu l , and of the D meson semileptonic decays D->(K/pi) nu l which are relevant for the extraction of the CKM matrix element |Vus|, |Vcd| and |Vcs| from experimental data. Our preliminary results are based on the gauge configurations produced by the European Twisted Mass Collaboration with Nf=2+1+1 dynamical fermions, which account for the sea quark effects of the up, down, strange and charm quarks. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV.

Speaker: Mr Lorenzo Riggio (INFN)

Slides Lorenzo_Riggio_Talk_LATTICE2014.pdf

385 Standrad Model contributions to B and Bs meson semileptonic decays

We present our recent results on B to D, Bs to Ds, and Bs to K Standard Model tree level semileptonic decays. We have used MILC Nf=2+1 asqtad gauge configurations with two lattice spacings. For the valence quarks, we used NRQCD bottom quarks and HISQ light and charm quarks. The B to D and Bs to Ds semileptonic form factors can be used for better determination of the Bs to [mu^+ mu^-] branching fraction. Furthermore the ratio R(D) of the B to [D, tau, nu] and B to [D, mu, nu] branching fractions is of considerable phenomenological interest since there currently exists some tension between experiment and Standard Model predictions for R(D). The Bs to K semileptonic decay is a new channel at LHCb and Belle II for alternate V_{ub} determinations. Our form factor results for this decay are the first from lattice QCD.

Speaker: Heechang Na (University of Utah)

Slides Heena.lat2014.pdf

386 Improved currents for B to D(*) ell nu form factors from Oktay-Kronfeld heavy quarks

The CKM matrix element |V_{cb}| can be extracted by combining experimentally determined branching fractions for B to D(*) ell nu decays with form factors from the lattice. While successful, the precision of this approach has been limited by heavy-quark discretization effects. An improved version of the Fermilab action, the Oktay-Kronfeld action, can be used to reduce heavy-quark discretization effects in calculations performed at the physical bottom and charm quark masses. Treating charm and bottom quarks as massive, we carry out tree-level improvement of the flavor-changing currents through third order in the momentum expansion.

Speaker: Jon Bailey (Seoul National University)

Slides jab_lat14.pdf

387 Non-perturbative study of the chromagnetic operator on the lattice

We describe our study of the chromomagnetic operator O_CM, which appears in the effective Hamiltonian describing DS=1 transitions in and beyond the Standard Model. Having dimension 5, the chromomagnetic operator is characterized by a rich pattern of mixing with other operators of equal and lower dimensionality. We have computed the coefficients of the mixing with the various dimension 5 operators using one loop lattice perturbation theory and determined the power-divergent mixing coefficient with the scalar density non-perturbatively. The numerical computations have been carried out by using the gauge configurations produced by the European Twisted Mass Collaboration with Nf = 2 + 1 + 1 dynamical quarks, at three values of the lattice spacing and several values of the light quark masses. In this talk, we will mainly describe the non-perturbative parts of the calculation and present preliminary results for the matrix element of the chromomagnetic operator between pion and kaon states.

Speaker: Vittorio Lubicz (Universita' Roma Tre)

Slides CMO_Lattice.pdf

Saturday, 28 June

Plenary

Convener: Prof. Constantia Alexandrou (University of Cyprus)

388 Lattice QCD with purely imaginary sources at zero and non-zero temperature.

Speaker: Prof. Massimo D'Elia (University of Pisa & INFN)

Slides lattice14_delia.pdf

389 QPACE 2 and Domain Decomposition on the KNC

I will give an overview of QPACE 2, which is a custom-designed machine based on Intel Xeon Phi processors, developed by Regensburg University in collaboration with Eurotech (Italy/Japan). I will also discuss our high-performance implementation of a domain-decomposition-based solver on the Xeon Phi and present benchmarks of its strong-scaling behavior.

Speaker: Prof. Tilo Wettig (University of Regensburg)

Slides lat14_final.pdf

390 Measurement of thermodynamics using Gradient Flow

We propose a novel method to define and calculate the energy-momentum tensor (EMT) in lattice gauge theory on the basis of the Yang-Mills gradient flow. Using this method, we measure the thermodynamics of SU(3) gauge theoy on fine lattices with lattice size up to 64^3x18. The numerical results with small lattice spacing confirm our previous findings; the expectation values of the EMT have reasonable dependences on the flow time near the continuum limit, and thus our method can successfully be applied to the analysis of the EMT on the lattice.

Speaker: Prof. Masakiyo Kitazawa (Osaka University)

Slides 1406LATTICE_GF2.pdf

10:00 Coffee Break

Plenary

Convener: Prof. Yoshinobu Kuramashi (Tsukuba University/CCS/AICS)

391 Long Distance Effects from the Lattice

Speaker: Prof. Chris Sachrajda (University of Southampton)

Slides Sachrajda_Latt14.pdf

392 Conference Closing