Matching pre-equilibrium dynamics and viscous hydrodynamics

TL;DR

This paper develops a method to seamlessly connect pre-equilibrium dynamics with viscous hydrodynamics in quark-gluon plasma, providing analytic formulas for initial conditions and analyzing entropy production effects.

Contribution

It introduces a matching procedure between pre-equilibrium models and viscous hydrodynamics, with analytic formulas for initial conditions based on different pre-equilibrium scenarios.

Findings

Matching conditions depend on pre-equilibrium model choice.

Analytic formulas for initial energy density and shear tensor.

Entropy production varies with pre-equilibrium dynamics.

Abstract

We demonstrate how to match pre-equilibrium dynamics of a 0+1 dimensional quark gluon plasma to 2nd-order viscous hydrodynamical evolution. The matching allows us to specify the initial values of the energy density and shear tensor at the initial time of hydrodynamical evolution as a function of the lifetime of the pre-equilibrium period. We compare two models for the pre-equilibrium quark-gluon plasma, longitudinal free streaming and collisionally-broadened longitudinal expansion, and present analytic formulas which can be used to fix the necessary components of the energy-momentum tensor. The resulting dynamical models can be used to assess the effect of pre-equilibrium dynamics on quark-gluon plasma observables. Additionally, we investigate the dependence of entropy production on pre-equilibrium dynamics and discuss the limitations of the standard definitions of the non-equilibrium entropy.