Phases of QCD

Recent years have seen an expansion of activities devoted to the study of the QCD phase diagram. The equation of state of strongly interacting matter is now at hand as a function of temperature T and in a limited range of quark chemical potential μ. In our work [1] we have studied the thermodynamics of two-flavour QCD at finite quark chemical potential. Our investigation is based on a synthesis of a Nambu Jona-Lasinio (NJL) model and the non-linear dynamics involving the Polyakov loop [2, 3]. In this Polyakovloop-extended (PNJL) model, quarks develop quasiparticle masses by propagating in the chiral condensate, while they couple at the same time to a homogeneous background (temporal) gauge field representing Polyakov loop dynamics. The main aim of our work is to investigate whether results from lattice QCD thermodynamics can be understood and interpreted in terms of quasiparticle degrees of freedom. The thermodynamic potential of the PNJL model is: