The hot non-perturbative gluon plasma is an almost ideal colored liquid

Abstract

We study properties of a gluon plasma above the critical temperature $T_c$ in a generalized quasi-particle approach with a Lorentz spectral function. The model parameters are determined by a fit of the entropy $s$ to lattice QCD data. The effective degrees of freedom are found to be rather heavy and of a sizeable width. With the spectral width being closely related to the interaction rate, we find a large effective cross section, which is comparable to the typical distance squared of the quasiparticles. This suggests that the system should be viewed as a liquid as also indicated by an estimate of the plasma parameter $\Gamma$. Furthermore, within the quasiparticle approach we find a very low viscosity to entropy ratio, $\eta/s \sim 0.2$ for $T > 1.05 T_c$, supporting the recent conjecture of an almost ideal quark-gluon liquid seen at RHIC.