Analysis of the chiral crossover in the phase diagram of 2+1-flavor Nambu–Jona-Lasinio model

In this paper, we study the Nambu-Jona-Lasinio model phase diagram for a 2+1 flavor quark system at finite temperature and chemical potential.We use various susceptibilities to obtain quantitatively different phase diagrams and analyze each one on the light and strange sectors, focusing on the first-order transition regions, critical points and, in greater detail, the crossover region. Although the current mass of the strange quark is very large, the overall behavior of the chiral symmetry restoration is qualitatively similar to the one of the light quarks. Also, due to the 't Hooft flavor-mixing interaction term, the strange quark transition is strongly influenced by the chiral restoration of the light sector, and we observe that the existing divergences of the susceptibilities around the CEP for light quarks appear also for the strange quark.We use two criteria for the delimitation of the crossover lines: one based on the inflection points of the order parameter, and another based on its absolute value. Also, we plot two crossover bands, one for the light quarks and another one for the strange quark through the use of the sign of the determinant of the Hessian matrix of the susceptibility surfaces.