Repulsive character induced by optimized perturbation techniques on the Polyakov-loop-extended Nambu—Jona-Lasinio model.

Abstract

Abstract The determination of the critical point on the QCD phase diagram depends experimentally on thermodynamic quantities related to the cumulants of the pressure. These quantities appear as coefficients in the Taylor expansion of the pressure and, specifically for the second order cumulant c 2, QCD results on the lattice (LQCD) show that it raises with the temperature towards the Stefan-Boltzmann limit. On the other hand, when one evaluates c 2 within quark effective models considering a repulsion on the vector channel parametrized by GV , this observable reaches a maximum just after Tc , deviating itself from LQCD predictions. Here we apply the Optimized Perturbation Theory (OPT) method to the two flavor Polyakov–Nambu–Jona-Lasinio model (at GV = 0) to confront our results with those furnished by LQCD simulations. We show that c 2 behaves satisfactorily at low-T and close to Tc , but, with GV ≠ 0, it develops a maximum at high-T. Our conclusions indicate that it would be possible that the correct high temperature behavior of c 2 beyond LN limit could be properly achieved by effective quark models if they also mimic the so-called asymptotic freedom phenomenon.