Non-congruence of the nuclear liquid-gas and deconfinement phase transitions

Abstract

First order phase transitions (PTs) with more than one globally conserved charge, so-called non-congruent PTs, have characteristic differences compared to congruent PTs (e.g., dimensionality of phase diagrams, location and properties of critical points and endpoints). In the present article we investigate the non-congruence of the nuclear liquid-gas PT at sub-saturation densities and the deconfinement PT at high densities and/or temperatures in Coulomb-less models, relevant for heavy-ion collisions and neutron stars. For the first PT, we use the FSUgold relativistic mean-field model and for the second one the relativistic chiral SU(3) model. The chiral SU(3) model is one of the few models for the deconfinement PT, which contains quarks and hadrons in arbitrary proportions (i.e. a "solution") and gives a continuous transition from pure hadronic to pure quark matter above a critical point. The study shows the universality of the applied concept of non-congruence for the two PTs with an upper critical point, and illustrates the different typical scales involved. In addition, we find a principle difference between the liquid-gas and the deconfinement PTs: in contrast to the ordinary Van-der-Waals-like PT, the phase coexistence line of the deconfinement PT has a negative slope in the pressure-temperature plane. As another qualitative difference we find that the non-congruent features of the deconfinement PT become vanishingly small around the critical point.