The characteristics of thermalization of boost-invariant plasma from holography

TL;DR

This study investigates how boost-invariant plasma approaches hydrodynamics at strong coupling using holography, revealing regularities and early effective thermalization despite initial anisotropies.

Contribution

It provides a detailed numerical analysis of thermalization in holographic plasma, highlighting correlations between initial entropy and thermalization properties, and suggesting earlier effective thermalization in heavy ion collisions.

Findings

Hydrodynamics applies after proper time > 0.7 inverse temperature units.

Strong correlations between initial entropy and thermalization temperature.

Early effective thermalization despite initial anisotropies.

Abstract

We report on the approach towards the hydrodynamic regime of boost-invariant N=4 super Yang-Mills plasma at strong coupling starting from various far-from-equilibrium states at tau=0. The results are obtained through numerical solution of Einstein's equations for the dual geometries, as described in detail in the companion article arXiv:1203.0755. Despite the very rich far-from-equilibrium evolution, we find surprising regularities in the form of clear correlations between initial entropy and total produced entropy, as well as between initial entropy and the temperature at thermalization, understood as the transition to a hydrodynamic description. For 29 different initial conditions that we consider, hydrodynamics turns out to be definitely applicable for proper times larger than 0.7 in units of inverse temperature at thermalization. We observe a sizable anisotropy in the energy-momentum tensor at thermalization, which is nevertheless entirely due to hydrodynamic effects. This suggests that effective thermalization in heavy ion collisions may occur significantly earlier than true thermalization.