Entropy production for an interacting quark-gluon plasma

TL;DR

This paper studies entropy production in relativistic heavy ion collisions using dissipative hydrodynamics with realistic equations of state and viscosity calculations, highlighting the complex interplay affecting initial state reconstruction.

Contribution

It introduces a consistent framework combining Israel-Stewart hydrodynamics, realistic QCD-inspired equations of state, and kinetic viscosity calculations for analyzing entropy production.

Findings

Viscosity and realistic EoS significantly influence entropy production.

Initial conditions are difficult to determine unambiguously from experimental data.

The interplay between viscosity and EoS affects the interpretation of heavy ion collision results.

Abstract

We investigate the entropy production within dissipative hydrodynamics in the Israel-Stewart (IS) and Navier-Stokes theory (NS) for relativistic heavy ion physics applications. In particular we focus on the initial condition in a 0+1D Bjorken scenario, appropriate for the early longitudinal expansion stage of the collision. Going beyond the standard simplification of a massless ideal gas we consider a realistic equation of state consistently derived within a virial expansion. The EoS used is well in line with recent three-flavor QCD lattice data for the pressure, speed of sound, and interaction measure at nonzero temperature and vanishing chemical potential ($\mu_{\rm q} = 0$). The shear viscosity has been consistently calculated within this formalism using a kinetic approach in the ultra-relativistic regime with an explicit and systematic evaluation of the transport cross section as function of temperature. We investigate the influence of the viscosity and the initial condition, i.e. formation time, initial temperature, and pressure anisotropy for the entropy production at RHIC at $\sqrt{s_{\rm NN}}=130$ GeV. We find that the interplay between effects of the viscosity and of the realistic EoS can not be neglected in the reconstruction of the initial state from experimental data. Therefore, from the experimental findings it is very hard to derive unambiguous information about the initial conditions and/or the evolution of the system.