Finite N corrections to the second order cumulant of pressure via the Optimized Perturbation Theory on the Nambu—Jona-Lasinio model

We show preliminary results for the second order cumulantof pressure at zero chemical potential, using the Nambu-Jona-Lasinio(NJL) model beyond traditional large-Nc (LN) or mean-field approximation (MFA). The main physical feature of this quantity lies on the determination of the critical point (CP) of the QCD phase diagram on the T — μ plane. Our calculations are done with the Optimized Perturbation Theory (OPT), which provides finite N corrections even in the first non-trivial order of perturbation. Also, the OPT generates dynamically the repulsive vector contribution, whose imposition in MFA has shown some weaknesses. Nevertheless, the results from both, once compared with those obtained by lattice QCD, suggest the need of a reformulation of the implementations near and above the critical temperature.