Relaxation time ansatz and shear and bulk viscosities of gluon matter

TL;DR

This paper calculates shear and bulk viscosities of gluon matter using a mean-field quasiparticle approach within the relaxation time approximation, analyzing the impact of different approximations and emphasizing the rough nature of these estimates.

Contribution

It introduces a non-equilibrium mean-field quasiparticle method to estimate gluon matter viscosities and assesses the robustness of these calculations against various approximations.

Findings

Shear viscosity results are robust across approximations.

Viscosity estimates within the relaxation time approximation are rough.

Different approximation schemes significantly affect bulk viscosity calculations.

Abstract

Shear and bulk viscosity-to-entropy density ratios are calculated for the pure gluon matter in a non-equilibrium mean-field quasiparticle approach within the relaxation time approximation. We study how different approximations used in the literature affect the results for the shear and bulk viscosities. Though the results for the shear viscosity turned out to be quite robust, all evaluations of the shear and bulk viscosities obtained in the framework of the relaxation time approximation can be considered only as rough estimations.