Hadronic chiral mean field models at extreme temperatures and densities

We study recently developed chiral mean field models under extreme conditions of temperature (T) and density (ρ). The thermal vacuum phase transition (ρ=0 and high T), present in the Walecka model, also appears in some of the proposed models. A hadronic phase transition to a quark-gluon plasma phase (QGP) at ρ≠0 is also shown in the T-ρ phase diagram. From this diagram we see that, at ρ=0, the critical temperature Tc is not sensitive to the employed hadronic model whereas when ρ increases and T decreases the hadronic-QGP two-phase transition becomes strongly model dependent. Particular cases of the models at zero temperature and high density are discussed. (author)