On the bulk viscosity of anisotropically expanding hot QCD plasma

TL;DR

This paper investigates the bulk viscosity of an anisotropically expanding hot QCD plasma, highlighting the significant role of interactions and anisotropy in determining viscous properties relevant for heavy-ion collision experiments.

Contribution

It introduces a model combining anisotropic gluon distributions with a quasi-particle approach to quantify bulk viscosity in hot QCD plasma.

Findings

Bulk viscosity arises from gluon momentum anisotropy.

Interactions in the equation of state significantly affect bulk viscosity.

Bulk viscosity ratio remains substantial at 1.5 times the critical temperature.

Abstract

The bulk viscosity, $\zeta$ and its ratio with the shear viscosity, $\zeta/\eta$ have been studied in an anisotropically expanding pure glue plasma in the presence of turbulent color fields. It has been shown that the anisotropy in the momentum distribution function of gluons, which has been determined from a linearized transport equation eventually leads to the bulk viscosity. For the isotropic (equilibrium) state, a recently proposed quasi-particle model of pure SU(3) lattice QCD equation of state has been employed where the interactions are encoded in the effective fugacity. It has been argued that the interactions present in the equation of state, significantly contribute to the bulk viscosity. Its ratio with the shear viscosity is significant even at $1.5 T_c$. Thus, one needs to take in account the effects of the bulk viscosity while studying the hydrodynamic expansion of QGP in RHIC and LHC.