Calculation of shear viscosity using Green-Kubo relations within a parton cascade

Understand

The shear viscosity of a gluon gas is calculated using the Green-Kubo relation.

• Time correlations of the energy-momentum tensor in thermal equilibrium are extracted from microscopic simulations using a parton cascade solving various Boltzmann collision processes.
• We find that the pQCD based gluon bremsstrahlung described by Gunion-Bertsch processes significantly lowers the shear viscosity by a factor of 3-8 compared to elastic scatterings.
• The shear viscosity scales with the coupling as 1/(alpha_s^2\log(1/alpha_s)).