TL;DR
This paper calculates the shear viscosity to entropy ratio in a gluon gas using relativistic kinetic theory, incorporating elastic and inelastic QCD scatterings, revealing low /s values indicative of strongly coupled systems.
Contribution
It derives a relation between shear viscosity and transport rate and computes /s for a gluon gas including bremsstrahlung effects, highlighting the impact of inelastic processes.
Findings
/s values are 0.13 at _s=0.3 and 0.076 at _s=0.6
Inelastic bremsstrahlung significantly reduces /s
Results suggest strongly coupled gluon systems
Abstract
The relation of the shear viscosity coefficient to the recently introduced transport rate is derived within relativistic kinetic theory. We calculate the shear viscosity over entropy ratio \eta/s for a gluon gas, which involves elastic gg-> gg perturbative QCD (PQCD) scatterings as well as inelastic gg<->ggg PQCD bremsstrahlung. For \alpha_s=0.3 we find \eta/s=0.13 and for \alpha_s=0.6, \eta/s=0.076. The small \eta/s values, which suggest strongly coupled systems, are due to the gluon bremsstrahlung incorporated.
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