Chiral crossover, deconfinement, and quarkyonic matter within a Nambu–Jona-Lasinio model with the Polyakov loop

We study the interplay between the chiral and the deconfinement transitions, both at high temperature and high quark chemical potential, by a nonlocal Nambu--Jona-Lasinio model with the Polyakov loop in the mean field approximation and requiring neutrality of the ground state. We consider three forms of the effective potential of the Polyakov loop: two of them with a fixed deconfinement scale, cases I and II, and the third one with a dependent scale, case III. In cases I and II, at high chemical potential and low temperature T, the main contribution to the free energy is due to the Z (3) -neutral three-quark states, mimicking the quarkyonic phase of the large N₂ phase diagram. On the other hand, in case III the quarkyonic window is shrunk to a small region. Finally we comment on the relations of these results to lattice studies and on possible common prospects. We also briefly comment on the coexistence of quarkyonic and color superconductive phases.