Color-flavor dependence of the Nambu-Jona-Lasinio model and QCD phase diagram

Abstract

We study the dynamical chiral symmetry breaking/restoration for the various numbers of light quarks flavors $N_f$ and colors $N_c$, using the Nambu-Jona-Lasinio (NJL) model of quarks, dressed with a color-flavor dependence of effective coupling. Initially, we set $N_f = 2$, and varying the number of colors $N_c$, we find that the dynamical chiral symmetry is broken when $N_c$ exceeds to its critical value $N^{c}_{c}\approx2.2$. Secondly, we take $N_c = 3$, and varying $N_f$, we observed that the dynamical chiral symmetry is restored when $N_f$ reaches to its critical value $N^{c}_{f}\approx8$. The strong interplay observed between $N_c$ and $N_f$, i.e., $N_c$ anti-screens the strong interactions by strengthening the dynamical mass and quark-antiquark condensate, while $N_f$ screens the strong interaction by suppressing both the parameters. We further sketch the quantum chromodynamics (QCD) phase diagram at finite temperature $T$ and quark chemical potential $\mu$ for various $N_c$ and $N_f$. At finite $T$ and $\mu$, we observed that the critical number of colors $N^{c}_c$ enhances while the critical number of flavors $N^{c}_f$ suppresses as $T$ and $\mu$ increases. Of course, the parameters $T$ and $\mu$ produce the screening effect. Consequently, the critical temperature $T_c$, $\mu_c$ and co-ordinates of the critical endpoint $(T^{E}_c,\mu^{E}_c)$ in the QCD phase diagram enhances as $N_c$ increases while suppresses when $N_f$ increases. Our findings agree with the Lattice QCD and Schwinger-Dyson equations predictions.