Shear viscosity of ultrarelativistic Boson systems in the presence of a Bose-Einstein condensate

TL;DR

This paper calculates the shear viscosity of ultrarelativistic Boson systems with a Bose-Einstein condensate using two methods, revealing that the BEC presence reduces viscosity, especially with higher BEC proportions.

Contribution

First calculation of shear viscosity in ultrarelativistic Boson systems with BEC using both Grad's method and Green-Kubo approach.

Findings

Bose-Einstein condensate lowers shear viscosity.

Higher BEC proportion further reduces viscosity.

Effect is insensitive to interaction details.

Abstract

We calculate for the first time the shear viscosity of ultrarelativistic Boson systems in the presence of a Bose-Einstein condensate (BEC). Two different methods are used. One is the Grad's method of moments and another is the Green-Kubo relation within a kinetic transport approach. In this work we consider a Boson system with isotropic elastic collisions and a gluon system with elastic scatterings described by perturbation QCD (pQCD). The results show that the presence of a BEC lowers the shear viscosity. This effect becomes stronger for the increasing proportion of the BEC in the Boson system and is insensitive to the detail of interactions.