Liquid-gas phase transition in strange hadronic matter with relativistic models

TL;DR

This study investigates how strangeness influences the nuclear liquid-gas phase transition using relativistic models, revealing that hyperons slightly suppress the transition and act as an order parameter, indicating instability of dilute strange matter.

Contribution

It provides a qualitative, model-independent analysis of strangeness effects on the nuclear liquid-gas phase transition using a relativistic mean field approach.

Findings

Hyperons slightly quench the liquid-gas phase transition.

Strangeness acts as an order parameter, indicating hyper-cluster formation.

Dilute strange matter is unstable against hyper-cluster formation.

Abstract

Background: The advent of new dedicated experimental programs on hyperon physics is rapidly boosting the field, and the possibility of synthetizing multiple strange hypernuclei requires the addition of the strangeness degree of freedom to the models dedicated to nuclear structure and nuclear matter studies at low energy. Purpose: We want to settle the influence of strangeness on the nuclear liquid-gas phase transition. Because of the large uncertainties concerning the hyperon sector, we do not aim at a quantitative estimation of the phase diagram but rather at a qualitative description of the phenomenology, as model independent as possible. Method: We analyze the phase diagram of low density matter composed of neutrons, protons and $\Lambda$ hyperons using a Relativistic Mean Field (RMF) model. We largely explore the parameter space to pin down generic features of the phase transition, and compare the results to ab-initio quantum Monte Carlo calculations. Results: We show that the liquid-gas phase transition is only slightly quenched by the addition of hyperons. Strangeness is seen to be an order parameter of the phase transition, meaning that dilute strange matter is expected to be unstable with respect to the formation of hyper-clusters. Conclusions: More quantitative results within the RMF model need improved functionals at low density, possibly fitted to ab-initio calculations of nuclear and $\Lambda$ matter.