We study the equation of state of hyperon-rich matter in neutron stars using an extended relativistic mean-field model. We take special care of the recently proposed nonlinear behavior of the vector field providing a much better agreement with Dirac-Brückner calculations. The hyperon-hyperon interaction is also implemented by introducing additional meson exchanges. With these new terms we avoid the instability found at high densities while keeping the excellent description for finite nuclear systems. We also demonstrate within the mean-field approach that the presence of hyperons inside neutron stars on one hand and the hyperon-hyperon interactions on the other hand make the onset of kaon condensation less favorable. © 1996 The American Physical Society.

We study the chiral phase transition at nonzero temperature T and baryon chemical potential ${\mu }_B$ within the framework of the linear sigma model and the Nambu–Jona-Lasinio (NJL) model. For small bare quark masses we find in both models a smooth crossover transition for nonzero T and ${\mu }_B=0\mathrm{}$ and a first order transition for $T=0\mathrm{}$ and nonzero ${\mu }_B.$ We calculate explicitly the first order phase transition line and spinodal lines in the $(T,{\mu }_B)$ plane. As expected they all end at a critical point. We find that, in the linear sigma model, the sigma mass goes to zero at the critical point. This is in contrast to the NJL model, where the sigma mass, as defined in the random phase approximation, does not vanish. We also compute the adiabatic lines in the $(T,{\mu }_B)$ plane. Within the models studied here, the critical point does not serve as a “focusing” point in the adiabatic expansion.