Recent thermodynamic results from lattice QCD analyzed within a quasi-particle model

Abstract

The thermodynamic behavior of QCD matter at high temperature is currently studied by lattice QCD theory. The main features are the fast rise of the energy density $\epsilon$ around the critical temperature $T_c$ and the large trace anomaly of the energy momentum tensor $< \Theta_\mu^\mu >=\epsilon - 3 P$ which hints at a strongly interacting system. Such features can be accounted for by employing a massive quasi-particle model with a temperature-dependent bag constant. Recent lattice QCD calculations with physical quark masses by the Wuppertal-Budapest group have shown a slower increase of $\epsilon$ and a smaller $<\Theta_\mu^\mu>$ peak with respect to previous results from the hotQCD collaboration. We investigate the implications of such differences from the point of view of a quasi-particle model, also discussing light and strange quark number susceptibilities. Furthermore, we predict the impact of these discrepancies on the temperature-dependence of the transport properties of matter, like the shear and bulk viscosities.Comment: 18 pages, 9 figures; version accepted in Phys. Rev.D; calculation with relaxation time \tau \sim g^4 ln g has been adde