Fluid dynamics of out of equilibrium boost invariant plasmas

TL;DR

This paper develops a moment-based framework for analyzing out-of-equilibrium boost-invariant plasmas, identifying an attractor solution that governs the transition to hydrodynamics and modifies the effective shear viscosity.

Contribution

It introduces a set of moment equations for the distribution function and demonstrates how to find an attractor solution that captures off-equilibrium effects on viscosity.

Findings

Identified an attractor controlling the transition to hydrodynamics.

Provided a method to renormalize shear viscosity considering off-equilibrium effects.

Demonstrated the applicability of moment equations in plasma dynamics.

Abstract

We establish a set of equations for moments of the distribution function. In the relaxation time approximations, these moments obey a coupled set of equations that can be truncated order-by-order. Solving the equations of moments, we are able to identify an attractor solution that controls a transition from a free streaming fixed point to a hydrodynamic fixed point. In particular, this attractor solution provides a renormalization of the effective value of the shear viscosity to entropy density ratio, $\eta/s$, taking into account off-equilibrium effects.