A key ingredient to model heavy ion collisions dynamically is the initial spatial distribution of protons and neutrons inside the nucleus. Traditionally in most theoretical calculations there is no difference between them and their positions are sampled with the Woods-Saxon distribution. However, this assumption has been invalidated by experimental measurements [1]: The diffusiveness of the...

Non-equilibrium Green's functions provide an efficient tool to describe the evolution of the energy-momentum tensor during the early time pre-equilibrium stage, and provide a meaningful to address the question when and to what extent a hydrodynamic description of the system becomes applicable. We present a calculation of the Green's functions describing the evolution of energy density...

The elliptic and triangular flow coefficients, $v_{2}$ and $v_{3}$, are expected to be driven by the initial anisotropy coefficients of the same order, $\epsilon_{2}$ and $\epsilon_{3}$, respectively. However, the higher order flow coefficients, $v_{n}$ (n $>$ 3), are comprised of linear contributions driven by $\epsilon_{n}$, as well as mode-coupled contributions derived from the lower order...

Relativistic viscous hydrodynamics has been an essential tool in studying the evolution of the Quark Gluon Plasma (QGP) produced in heavy-ion collisions as well as in searching for the critical point expected to be present for more baryon dense systems. With the coming runs of the Beam Energy Scan II at the Relativistic Heavy Ion Collider (RHIC), it will be necessary to implement conserved...

Various microscopic models suggest that local rest frame momentum anisotropies can be large during the early stages of evolution of the quark-gluon plasma (QGP). In recent years, the framework of relativistic anisotropic hydrodynamics (aHydro) has been developed in order to incorporate momentum anisotropic distributions of the QGP constituents into the phenomenological studies of...

We study the heavy-quark momentum diffusion coefficient in gluon plasmas in a self-similar regime using real-time lattice techniques. We observe that the time-evolution of the momentum diffusion coefficient is consistent with a t^(-5/7) power law, as predicted by HTL perturbation theory and self-similarity. Using HTL with our recently acquired data on the spectral function of over-occupied...

Anisotropic flow is well understood as a hydrodynamic response to spatial anisotropies in the system density at early times. This response function can be written explicitly as a systematic expansion in terms of length scales, such that the leading contribution is the familiar eccentricity $\varepsilon_n$ that represents global structure. These relations have allowed for direct connections...

We investigate the importance of different features of the initial geometry to anisotropic flow fluctuations in heavy-ion collisions. To that end, we explore the hydrodynamic response of differential flow harmonics $v_n(p_T)$ to generalized eccentricities $\epsilon_{n,m}$ of the initial density profile within a realistic hydrodynamic model. Special attention is paid to two-particle angular...

One of the primary goals of flow studies in heavy-ion collisions during recent years is a better understanding of the transport properties of the quark-gluon plasma (QGP), such as the temperature dependence of the shear viscosity to entropy ratio, $\eta/s(T)$. Flow observables, such as the higher order harmonics (n>3) and their non-linear responses to the initial state anisotropy have a strong...

In proton-nucleus collisions, the top quark is a novel and theoretically precise probe of the nuclear gluon density at high virtualities $Q^2\approx m_{\mathrm{top}}$ and in the less explored high Bjorken-$x$ region. The first observation of the inclusive $\mathrm{t\bar{t}}$ production has been performed using 174$\pm$6 $\mathrm{nb}^{-1}$ of data in pPb collisions at $\sqrt{\smash...

The Large Hadron-electron Collider (LHeC) is a proposed upgrade of the

LHC at CERN. An ERL will provide electrons to collide with the HL-LHC,

HE-LHC and the FCC-hh proton beams to achieve centre-of-mass energies

1.3-3.5 TeV and luminosities $~10^{34}$ cm$^{-2}$s$^{-1}$. They will

enlarge the kinematic plane by more than one order of magnitude

towards smaller $x$ and larger $Q^2$ than HERA. DIS...

The sPHENIX detector at RHIC, together with the accelerator's unique

capabilities, will enable a spectrum of new or improved measurements

enhancing our understanding of the initial state for nuclear

collisions. Specifically, sPHENIX measurements in spin polarized

proton-proton and proton-nucleus collisions will reveal more about how

partons behave in a nuclear environment, explore spin-spin...

Computing observables in high-energy collisions requires a functional average over the configurations of small-x gluons in the wave functions of the colliding hadrons. We discuss a method for performing biased averages, for example due to a multiplicity or centrality bias, where the gluon distributions of the hadrons are modified from their unbiased average. We consider specifically potential...

In relativistic kinetic theory, the one-particle distribution function is approximated by an asymptotic perturbative power series in Knudsen number which is divergent. For the Bjorken flow, we expand the distribution function in terms of its moments and study their nonlinear evolution equations. The resulting coupled dynamical system can be solved for each moment consistently using a...

Ever since the discovery of the quark-gluon plasma (QGP) the location of the critical point in the QCD phase diagram - the end point of the supposed first-order transition between hadronic matter and the QGP - has been a principal research goal for heavy-ion collision experiments at RHIC. We use the gauge/gravity duality to study a four-dimensional, strongly-coupled gauge theory with a...

Recently collected data by the ATLAS experiment at the LHC offer opportunities to explore dynamic properties of quark-gluon plasma. A new tool to study these properties is the modified Pearson's correlation coefficient, $\rho$, that quantifies the correlation between the mean transverse momentum in an event,[$p_\mathrm{T}$], and the square of the flow harmonic magnitude, $v_n^2$. To suppress...

An ongoing question in the field is if the collectivity originating in small systems arises from:

- Flow scenario: initial conditions coupled to relativistic hydrodynamics leading to independent particle emissions from the fluid hyper-surface.

or

- Non-flow scenario: genuine 2,4 etc particle correlations from, e.g. a saturation framework.

We note that, in general, the experimentally...

Two particle correlations have been used extensively to study hydrodynamic flow patterns in heavy-ion collisions. In small collision systems, such as p+p and p+A, where particle multiplicities are much smaller than in A+A collisions, non-flow effects from jet correlations, momentum conservation, particle decays, etc. can be significant, even when imposing a large pseudorapidity gap between the...

Centrality fluctuations is one of the main uncertainties for interpreting the centrality dependence of many experimental observables. The centrality fluctuation is constrained by selection based on particle multiplicity in a reference subevent, and contributes to observables measured in another subevent. Due to the asymmetry between forward- and backward-going participating nucleons, the...

We present the first computation of the NLO photon+dijet impact factor in e+A DIS at small $x$. When combined with the recent derivation of JIMWLK small $x$ evolution to NLL$x$ accuracy, this result provides us with a prediction of the photon+dijet cross-section in e+A DIS to

O($\alpha_S^3 \ln(1/x)$) accuracy. The comparison of this result with photon+dijet measurements at a future EIC...

The proposed high-luminosity high-energy Electron Ion Collider (EIC) will provide one of the cleanest environments to precisely determine the nuclear parton distribution functions (nPDFs) in a wide x-$Q^{2}$ phase space. Heavy flavor production at the EIC can access up to the confinement boundary, which allows us to directly study nPDFs, quark/gluon fragmentation processes, and energy loss...

I discuss conformal properties of TMD operators and present the

result of the conformal rapidity evolution of TMD operators in the Sudakov region

The observed azimuthal modulations of long-range correlations in pseudorapidity in small systems like pp or p-Pb collisions show strikingly similar features to those seen in heavy ion collisions. Many theoretical approaches to interpreting this effect have been developed. However, it is still unclear whether these long-range correlations are due to final or initial state effects.

To further...

Hydro simulations are compared with recent experimental data by CMS, on a Principle Component Analysis. The trends for the scaled leading and sub-leading components for n=2,3 agree with data. In contrast, for n=0 there is a qualitative disagreement: the leading component increases with $p_T$ while it is constant in data. Using a toy model where the principal components can be computed...

ALICE has performed several measurements aimed at understanding the heavy-ion-like patterns observed in small collision systems. New approaches can be helpful to clarify particle production mechanisms in pp collisions, as well as the similarities observed among the systems created in pp, p-A and A-A collisions.

In this talk we report on charged-particle transverse momentum distributions as a...