Discussion of thermodynamic features within the PNJL model**Supported by National Natural Science Foundation of China (11475085, 11535005, 11690030, 11805097), National Major state Basic Research and Development of China (2016YFE0129300) and Jiangsu Provincial Natural Science Foundation of China (BK20180323)

Abstract

We discuss some thermodynamical features of a QCD system within the two-flavor Polyakov loop extended Nambu–Jona-Lasinio (PNJL) model. Several thermodynamical quantities of interest (pressure, energy density, specific heat, speed of sound, etc.) are investigated and discussed in detail with two different forms of Polyakov loop potential. The effective coupling strength G incorporating a quark feedback (quark condensate) through operator product expansion is also discussed, as well as the relationship between color deconfinement and chiral phase crossover. We find that some thermodynamical quantities have quite different behavior for different Polyakov loop potentials. By changing the characteristic temperature T0 of the pure Yang-Mills field, we find that when T0 becomes small, color deconfinement might happen earlier than chiral phase crossover, while their relationship can be determined via some thermodynamical quantities. Furthermore, the behavior of the thermodynamical quantities is quite different in the two different forms of Polyakov loop potential studied. Especially, one of the potentials, specific heat, has two peaks, which correspond to color deconfinement and chiral phase crossover respectively. This interesting phenomenon may shed some light on whether the inflection points of the chiral condensate and deconfinement transitions happen at the same temperature or not for lattice QCD and experimental studies.