Viscosity and thermodynamic properties of QGP in relativistic heavy-ion collisions

We study the viscosity and thermodynamic properties of QGP at RHIC by employing the recently extracted equilibrium distribution functions from two hot QCD equations of state of O(g 5) and O(g 6ln (1/g)), respectively. After obtaining the temperature dependence of the energy density and the entropy density, we focus our attention on the determination of the shear viscosity for a rapidly expanding interacting plasma, as a function of temperature. We find that the interactions significantly decrease the shear viscosity. They decrease the viscosity to entropy density ratio, η/S as well. (orig.)