# Open Problems and Opportunities in Chiral Fluids

US/Arizona
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Description

Macroscopic manifestations of the chiral anomaly have attracted significant attention in the last decade opening up multiple new directions of research. The various developments in this field include but are not limited to chiral effects in hot quark gluon plasma, cold dense matter in astrophysical environments as well as Dirac semimetals in condensed matter systems. The anomalous dynamics and polarization effects in these systems have also posed a variety of formal questions with regards to the interplay between different branches of theoretical physics.

The goal of this workshop is to provide a platform to researchers exploring physics of these systems to interact and engage in discussions leading to cross fertilization of ideas. The workshop aims to bring together senior researchers, postdoctoral fellows and graduate students to create a vibrant and exciting academic atmosphere that will unlock future directions in the field.

This workshop will serve as a platform to share ideas related to the chiral transport between various different fields such as astrophysics, heavy-ion collisions, condensed matter, and cold atom physics. The cross-field interaction is especially important now when the progress is fast both on the theoretical and experimental sides.

This is the Indico page used to manage the schedule and contributions for this event.

Registration and further useful informations about this event and the surrounding Santa Fe area are found on the main cvent-page for this event:

www.cvent.com/d/ygqn6d

You can contact the organizers via:

chiralfluids@lanl.gov

Contact
• Monday, 16 July
• 12:00 18:00
Arrival (not an official event) 6h
• Tuesday, 17 July
• 08:15 09:00
Welcome/Breakfast 45m
• 09:00 09:10
Opening remarks 10m
Speakers: Andrey Sadofyev (LANL, T-2) , Niklas Mueller (Brookhaven Nation Lab) , Raju Venugopalan (BNL) , Srimoyee Sen (University of Washington)
• 09:10 09:45
Searches for chiral fluids in relativistic nuclear collisions at the LHC with the CMS experiment. 35m

I will discuss recent experimental studies in search for the chiral magnetic effect and chiral magnetic wave in pPb and PbPb collisions at the LHC with the CMS experiment.

Speaker: Wei Li (Rice University)
• 09:45 10:20
Chiral Anomaly and Berry's Phase 35m

We define adiabatic Berry's phase precisely following the original ideas of Berry and Simon such that its topology arises from the singularity associated with the level crossing phenomenon. This definition covers most of the popular examples of Berry's phase such as Stone's model and
the model of Xiao, Shi and Niu, but their validity domains are severely limited. Part of the freedom of the 'monopole' associated with Berry's adiabatic phase is frozen compared to the conventional monopole, and we suggest a term 'adiabatic monopole'. A well-defined monopole is not derived from an adiabatic monopole. This limitation implies that the kinematical derivation of the covariant gauge anomaly from Berry's phase via an adiabatic monopole in the literature is not justified, besides the cavariant gauge anomaly thus derived does not satisfy the 'anomaly matching condition'

Speaker: Kazuo Fujikawa
• 10:20 10:55
Hydrodynamic modes in charged chiral plasmas with vorticity 35m

By making use of a covariant formulation of the chiral kinetic theory in the relaxation-time approximation, the first-order dissipative hydrodynamics equations for charged chiral plasma are derived. By solving the hydrodynamic equations, supplemented by the Maxwell equations, the spectra of hydrodynamic modes in a rotating chiral plasma in the regimes of high temperature and high density will be discussed. It is argued that nonzero vorticity has profound effects on both the global equilibrium state of the plasma and the spectrum of its hydrodynamic modes.

Speaker: Igor Shovkovy (Arizona State U)
• 10:55 11:25
Coffee Break 30m
• 11:25 12:00
Tunable circular dichroism due to the chiral anomaly in Weyl semimetals 35m

Weyl semimetals are a three-dimensional gapless topological phase in which bands intersect at arbitrary points (the Weyl nodes) in the Brillouin zone. These points carry a topological quantum number known as the chirality and always appear in pairs of opposite chiralities. The notion of chirality leads to anomalous nonconservation of chiral charge, known as the chiral anomaly, according to which charge can be pumped between Weyl nodes of opposite chiralities by an electromagnetic field with nonzero $\mathbf{E}\cdot\mathbf{B}$. Here, we propose probing the chiral anomaly by measuring the
optical activity of Weyl semimetals via circular dichroism. In particular, we observe that applying such an electromagnetic field on this state gives it a nonzero gyrotropic coefficient or a Hall-like conductivity, which may be detectable by routine circular dichroism experiments. This method also serves as a diagnostic tool to discriminate between Weyl and Dirac semimetals; the latter will give a null result. More generally, any experiment that probes a bulk correlation function that has the same symmetries as the gyrotropic coefficient can detect the chiral anomaly as well as differentiate between Dirac and Weyl semimetals.

Speaker: Pavan Hosur (U of Houston)
• 12:00 12:35
Energy Conservation and the Chiral Magnetic Effect 35m

We analyze the chiral magnetic effect in a homogeneous neutral plasma from the point of view of energy conservation, and construct an effective potential for the growth of maximally helical perturbations of the electromagnetic field. We show that a negative curvature at the origin of the potential, indicating instability of the plasma, is induced by a chiral asymmetry in electron Fermi energy, as opposed to number density, while the potential grows at large field value. It follows that the ground state for a plasma has zero magnetic helicity; a nonzero electron mass will allow an excited state of a plasma with nonzero helicity to relax to that ground state quickly. We conclude that a chiral plasma instability triggered by weak interactions is not a viable mechanism for explaining magnetic fields in stars except possibly when dynamics drives the system far from equilibrium.

Speaker: Srimoyee Sen (University of Washington)
• 12:35 14:00
Lunch Break 1h 25m
• 14:00 14:35
An Experimental Overview on Chiral Fermion Transport in Condensed Matters 35m

Recent discoveries of new phenomena due to interacting chiral fermions across vastly different energy and length scales have led to a fascinating convergence between condensed matter physics and high energy nuclear physics. The powerful notion of chirality underpins a wide palette of new and useful phenomena. Chiral magnetic effect has been discovered in condensed matter systems, enabling chiral charges to travel without resistance, provided chirality is conserved. Berry curvature of Weyl notes produces large anomalous Hall and Nernst effect. Mixed axial–gravitational anomaly provides a distinct contribution to a chiral imbalance, leading to a positive magneto-thermoelectric conductance for Weyl fermions,. Detection and manipulation of Weyl fermions by optical means has been demonstrated, leading to the proposal of chiral qubit. In this presentation, I will give an overview on experimentally probing chiral fluids in condensed matters, discuss their robustness and the prospect of harnessing the power of chirality for transport of energy and quantum information at room temperature.

Speaker: Qiang Li (BNL)
• 14:35 15:10
Cosmology with a chiral flavor 35m

Whether the parity of the Universe is broken on the large scale is an ongoing question. If this is the case, then one may trace the origin of parity violation back to the inflationary era. In this talk, I will review a few mechanisms that lead to the generation of helical fields, a source of breaking the parity on the large scale. The presence of helical U(1) fields in the early Universe can explain the baryon asymmetry of the Universe. In fact, there is a connection between the baryon number and topology of the relic magnetic part of the U(1) field. Both the magnitude and sign of magnetic helicity can be detected in future diffuse gamma ray data. This will be a smoking gun for a link between inflation, parity violating fields, and the baryon asymmetry of the Universe.

Speaker: Mohammed Anber (Lewis & Clark)
• 15:10 15:40
Coffe Break 30m
• 15:40 16:15
TBA 35m
Speaker: Emil Mottola (LANL, T-2)
• 16:15 16:50
World-line Approach to Chiral Kinetic Theory and the Chiral Magnetic Effect 35m

Recent searches for CP- and P- odd phenomena in ultra relativistic heavy-ion collisions have attracted much interest and are a prime motivation for significant theoretical effort. Anomalous and topological effects, such as the Chiral Magnetic Effect (CME), receive important contributions from the pre-equilibrium phase of a collision. While real-time lattice simulations can be used to study the earliest stage, quantitative predictions of experimental signatures are only feasible once the subsequent transport of the messengers of the CME through the fireball are understood. An interesting question is how the chiral imbalance generated at early times persists through a fluctuating background of sphalerons in addition to other "non-anomalous" interactions with the QGP. To address this question, we construct a relativistic chiral kinetic theory using the world-line formulation of quantum field theory. Using this framework we clarify the role of a possible Berry’s phase and that of the chiral anomaly. We discuss how the fate of the Chiral Magnetic Effect
could be understood by matching our framework to the results of real-time lattice simulations at early times and to Chiral MagnetoHydrodynamics at late times.

Speaker: Niklas Mueller (Brookhaven Nation Lab)
• 16:50 17:10
Break 20m
• 17:10 17:40
Discussion Session 30m
• Wednesday, 18 July
• 08:15 09:00
Working Breakfast 45m
• 09:00 09:35
Search for chiral effects at the RHIC 35m

In this talk, I will present the recent results from the STAR experiment towards the search for the chiral effects in p/d+Au, Au+Au and U+U collisions. I will also briefly discuss the status of the ongoing Isobar run at the RHIC.

Speaker: Prithwish Tribedy (BNL)
• 09:35 10:10
Chiral currents from Anomalies 35m

I will explore some aspects of how the currents in the Chiral Magnetic and Chiral Vortical Effects (CME and CVE) arise from the underlying anomalies. In particular I will show how the $T^2$ contribution to the Chiral Vortical Effect arises from the Pontryagin-density contribution to the axial anomaly, and also how this contribution itself emerges from geomteric phase shifts as a Chiral Weyl particle navigates through twisted space-time.

Speaker: Michael Stone (University of Illinois)
• 10:10 10:45
Hydrodynamics and QCD Critical Point in Magnetic Field 35m

The key features of hydrodynamics of QCD plasma in the presence of magnetic field is reviewed in both cases of dynamical and non-dynamical electromagnetism. We present a computation of shear viscosity for the non-dynamical electromagnetism case in perturbative QCD in leading log for soft magnetic fields. We then discuss possible modification of the dynamic universality class of QCD critical point in the presence of non-dynamical magnetic field.

Speaker: Ho-Ung Yee (University of Illinois at Chicago)
• 10:45 11:15
Coffee Break 30m
• 11:15 11:50
Disentangling covariant Wigner functions for chiral fermions 35m

We develop a general formalism for the quantum kinetics of chiral fermions in a background electromagnetic field based on a semiclassical expansion of covariant Wigner functions in the Planck constant $\hbar$. We demonstrate to any order of $\hbar$ that only the time-component of the Wigner function is independent while other components are explicit derivatives. We further demonstrate to any order of $\hbar$ that a system of quantum kinetic equations for multiple-components of Wigner functions can be reduced to one chiral kinetic equation involving only the single-component distribution function. These are remarkable properties of the quantum kinetics of chiral fermions and will significantly simplify the description and simulation of chiral effects in heavy ion collisions and Dirac/Weyl semimetals. We also present the chiral kinetic equations in four-momentum up to $O(\hbar ^2)$. We find that the chiral anomaly may come from a new source in the chiral kinetic equation, in contrast to the well-known scenario of the Berry phase term.

Speaker: Qun Wang (University of science and technology of China)
• 11:50 12:25
Condensed matter systems with anomalies 35m

We have a good theoretical understanding of transport due to quantum anomalies. Nevertheless, experimental realization of such a transport in high-energy systems is notoriously difficult. In my talk I will present promising candidates at low energies that may exhibit anomalous transport. These include conventional Weyl semi-metals as well as generalizations thereof, such as multi-Weyl semi-metals, tilted Weyls semi-metals and systems with higher spin quasi-particles. I will introduce these models and show the opportunities and challenges they present.

Speaker: Piotr Surowka (Dresden Max Planck)
• 12:25 14:00
Lunch Break 1h 35m
• 14:00 14:35
Aspects of electrodynamics in hot nuclear matter 35m

Hot nuclear matter contains metastable CP-odd domains induced by the topological gluon field fluctuations. Because of the chiral anomaly, quantum electrodynamics couples to these domains which results in a number of new electromagnetic effects. I discuss the role of realistic boundary conditions on the charge separation in heavy-ion collisions and the radiative instability of single-particle states.

Speaker: Kirill Tuchin (Iowa)
• 14:35 15:10
On-shell effective field theory and the chiral kinetic equation 35m

I will address the derivation of the chiral kinetic theory and the chiral anomaly for massless fermions using quantum field theory techniques. For this goal, we have developed the so-called on-shell effective field theory (OSEFT) expressed in an arbitrary reference frame. This effective theory accounts for nearly on-shell fermions and antifermions, while the off-shell degrees of freedom are integrated out. This provides a systematic expansion of the Lagrangian in inverse powers of the on-shell energy. We derive the collisionless kinetic equation for the fermion Wigner function, obtaining the necessary corrections to reproduce the chiral magnetic effect, anomalous Hall current... and the consistent form of the chiral anomaly equation. The Lorentz invariance of the OSEFT is analyzed by means of the reparametrization invariance of the effective Lagrangian. Applying reparametrization transformations to the Wigner function we automatically obtain the peculiar Lorentz transformation of the distribution function, originated by the so-called fermion side jumps.

Speaker: Dr Juan Torres-Rincon (Stony Brook University)
• 15:10 15:40
Coffee Break 30m
• 15:40 16:15
Anomalous hydrodynamics from projection operator method 35m

Anomalous hydrodynamics is a low-energy effective theory that captures anomaly-induced transport such as the chiral magnetic effect. Although there are several derivations of anomalous hydrodynamic equation from microscopic quantum theory, it has been unclear how we can derive it based on the operator formalism of quantum theory. In this talk, we derive anomalous hydrodynamic equation based on so-called Mori's projection operator method, which provides a systematic way to derive the equation of motion for slow variables like conserved charge densities in hydrodynamics. The vital point for Mori's projection operator method is that it gives a generalization of the current algebra technique used in low-energy hadron dynamics of the QCD vacuum to the nonequilibrium situations. As a result, we find that the chiral magnetic effect is caused by the anomalous commutation relation between vector and axial charge densities which represents a manifestation of the quantum anomaly in the operator formalism. We further discuss an extension of our derivation to the symmetry-broken phase which brings about anomalous superfluid hydrodynamics.

Speaker: Masaru Hongo (RIKEN)
• 16:15 16:50
Relativistic hydrodynamics with spin 35m

A new framework for relativistic hydrodynamics with spin is proposed. It is based on the conservation laws for charge, energy, momentum, and angular momentum. The conservation laws lead to hydrodynamic equations for the charge density, local temperature, and fluid velocity, as well as for the spin polarization tensor. The resulting set of differential equations extends the standard picture of perfect-fluid hydrodynamics, with a conserved entropy current, in a minimal way.

Speaker: Enrico Speranza (Frankfurt)
• 16:50 17:25
Chiral Magnetic Effect in Graphene? 35m

Graphene consists of a single layer of carbon atoms tightly packed into a honeycomb lattice and it was the first material where the charge carriers were observed to have a relativistic-like behavior. Its structure is suitably represented as an overlap of two triangular sublattices, giving rise to a degree of freedom analogous to the spin, the so-called pseudo-spin. Unlike the spin, the pseudo-spin is usually considered as an unmeasurable quantity, immune to Stern-Gerlach-type of experiment. In certain circumstances, however, there are some evidence that pseudo-spin could be associated to actual angular momentum. Under these circumstances, I propose that the chiral magnetic effect might take place in this material, similarly to what is observed in Weyl materials.

Speaker: Ana Julia Silveira Mizher (KU Leuven)
• 17:25 17:40
Break 15m
• 17:40 18:10
Final Discussion Session 30m
• Thursday, 19 July
• 08:15 09:00
Working Breakfast 45m
• 09:00 09:35
CME & CVE neutron star kicks, thermodynamic chiral transport, and polarization 35m

We argue that the standard chiral magnetic effect (CME) and potentially the chiral vortical effect (CVE) can lead to large momentum gains which were observed in proto neutron stars, also called neutron star kicks. This effect is of linear order in derivatives in a hydrodynamic derivative expansion. Beyond that, we systematically derive order zero in derivative CME and CVE, and calculate both explicitly in a holographic model. Finally, we discuss implications of this systematic treatment for the polarization of hot charged plasma potentially subjected to a magnetic field and with vorticity, such as the quark gluon plasma generated in a heavy ion collision.

Speaker: Matthias Kaminski
• 09:35 10:10
Effective field theory for Anomalous Hydrodynamics 35m

I will show how the recently developed formulation of non-equilibrium effective field theory can be implemented to write an effective action for anomalous hydrodynamics. This formulation has the advantage that traditional phenomenological constraints are derived from first principles, and that hydrodynamic fluctuations can be treated systematically. In particular, I will show how anomalous transport, such as the chiral magnetic effect, arises from basic symmetry requirements. I will also outline the relation between these effective field theories and global anomalies.

Speaker: Paolo Glorioso (The University of Chicago)
• 10:10 10:45
The Vortical Zilch 35m

For fermions the chiral vortical effect is well established theoretically. A similar effect has been suggested for a gas of photons at finite temperature. We investigate this effect by considering Maxwell theory in a rotating cylinder. Similarities and differencies to the fermionic case will be discussed and we will give a use to the Zilch!

Speaker: Karl Landsteiner (Instituto de Física Teórica UAM-CSIC)
• 10:45 11:20
Dynamics of vortices in chiral media 35m

We study the motion of vortex filaments in chiral media. The dynamics of the filament is described by a modified version of the localized induction equation in the parity-breaking background, which can be mapped to the integrable Hirota equation. We analyze physical properties such as the modification of solutions and fluctuations around them.

Speaker: Yuji Hirono (Brookhaven National Laboratory)
• 11:20 11:30