Coupling hydrodynamics to nonequilibrium degrees of freedom in strongly interacting quark-gluon plasma

TL;DR

This paper extends relativistic hydrodynamics models of quark-gluon plasma by incorporating nonequilibrium degrees of freedom via AdS/CFT, improving accuracy in pre-equilibrium dynamics simulations.

Contribution

It introduces new evolution equations that couple hydrodynamics with far-from-equilibrium modes using holography, enhancing modeling of early plasma evolution.

Findings

New equations match MIS theory near hydrodynamic regime

More accurately describe pre-equilibrium dynamics

Validated with holographic simulations of N=4 super Yang-Mills plasma

Abstract

Relativistic hydrodynamics simulations of quark-gluon plasma play a pivotal role in our understanding of heavy ion collisions at RHIC and LHC. They are based on a phenomenological description due to Mueller, Israel, Stewart (MIS) and others, which incorporates viscous effects and ensures a well-posed initial value problem. Focusing on the case of conformal plasma we propose a generalization which includes, in addition, the dynamics of the least damped far-from-equilibrium degree of freedom found in strongly coupled plasmas through the AdS/CFT correspondence. We formulate new evolution equations for general flows and then test them in the case of N=4 super Yang-Mills plasma by comparing their solutions alongside solutions of MIS theory with numerical computations of isotropization and boost-invariant flow based on holography. In these tests the new equations reproduce the results of MIS theory when initialized close to the hydrodynamic stage of evolution, but give a more accurate description of the dynamics when initial conditions are set in the pre-equilibrium regime.