Fluid dynamics of out of equilibrium boost invariant plasmas

TL;DR

This paper demonstrates how a simplified kinetic model can exactly reproduce the dynamics of viscous hydrodynamics, explaining why hydrodynamics works well even far from equilibrium.

Contribution

It establishes a precise connection between kinetic theory and viscous hydrodynamics using a simplified model, clarifying the success of hydrodynamics out of equilibrium.

Findings

Exact correspondence between kinetic equations and viscous hydrodynamics hierarchy.

Insight into the mechanisms behind hydrodynamics' success far from equilibrium.

A simplified kinetic model captures complex plasma dynamics.

Abstract

By solving a simple kinetic equation, in the relaxation time approximation, and for a particular set of moments of the distribution function, we establish a set of equations which, on the one hand, capture exactly the dynamics of the kinetic equation, and, on the other hand, coincide with the hierarchy of equations of viscous hydrodynamics, to arbitrary order in the viscous corrections. This correspondence sheds light on the underlying mechanism responsible for the apparent success of hydrodynamics in regimes that are far from local equilibrium.