Far-from-equilibrium attractors in kinetic theory with two different relaxation times

TL;DR

This paper investigates the early- and late-time attractors in the evolution of quark-gluon fluids out of equilibrium, revealing their emergence before hydrodynamics becomes applicable and analyzing entropy production under various initial conditions.

Contribution

It introduces a numerical study of kinetic theory with two relaxation times, identifying attractors in out-of-equilibrium quark-gluon systems and reconstructing their distribution functions.

Findings

Identification of early- and late-time attractors in kinetic evolution.

Reconstruction of full distribution functions from moments.

Analysis of entropy production dynamics.

Abstract

We solve a Boltzmann equation for massless quark and gluon fluids in a transversally homogeneous, longitudinally boost-invariant expansion. Quarks can be out of chemical equilibrium and the relaxation times of the two species are assumed to be connected by Casimir scaling. We numerically calculate moments of the distribution functions, identifying their early- and late-time attractors and reconstructing also the full distributions. These attractors appear when the system is still far from local thermalization, before hydrodynamics traditionally would be expected to apply. We also analyze the evolution of entropy production for different initial momentum anisotropies and quark abundances.