Phase transitions in a chiral model of nuclear matter

Abstract

The phase structure of symmetric nuclear matter in the extended Nambu--Jona-Lasinio (ENJL) model at finite baryon chemical potential ${\ensuremath{\mu}}_{{\phantom{\rule{-0.16em}{0ex}}}_{B}}$ and temperature $T$ is studied by means of the effective potential in the one-loop approximation. It is found that chiral symmetry gets restored at high nuclear density and a typical first-order phase transition between liquid and gas occurs at zero temperature, $T=0$, which weakens as $T$ grows and eventually ends up with a critical point at $T\ensuremath{\lesssim}18$ MeV. This phase transition scenario is confirmed by investigating the evolution of the effective potential as a function of effective nucleon mass and the equation of state. The restoration of chiral symmetry gives a second-order phase transition in the region $0\ensuremath{\leqslant}T\ensuremath{\lesssim}171$ MeV and a first-order transition in the region $T\ensuremath{\gtrsim}171$ MeV.