Asymmetric nuclear matter in a parity doublet model with hidden local symmetry

We construct a model to describe dense hadronic matter at zero and finite temperatures, based on the parity doublet model of DeTar and Kunihiro [C. E. DeTar and T. Kunihiro, Phys. Rev. D 39, 2805 (1989)], including the isosinglet scalar meson sigma as well as rho and omega mesons. We show that, by including a six-point interaction of the s meson, the model reasonably reproduces the properties of normal nuclear matter with the chiral invariant nucleon mass m(0) in the range from 500 to 900 MeV. Furthermore, we study the phase diagram based on the model, which shows that the value of the chiral condensate drops at the liquid-gas phase transition point and at the chiral phase transition point. We also study asymmetric nuclear matter and find that the first-order phase transition for the liquid-gas phase transition disappears in asymmetric matter and that the critical density for the chiral phase transition at nonzero density becomes smaller for larger asymmetry.