SU(3) parity doubling in cold neutron star matter

TL;DR

This paper develops a phenomenological SU(3) model to study parity doubling and chiral phase transitions in cold neutron star matter, revealing a mild first-order transition and implications for neutron star properties and evolution.

Contribution

It introduces a novel SU(3) based model incorporating baryonic degrees of freedom and parity partners, constrained by astrophysical data, to explore chiral symmetry restoration in neutron stars.

Findings

First-order phase transition within realistic L values.

Parity partner suppresses strangeness, delaying hyperonization.

Surface tension strongly depends on the chiral-invariant mass.

Abstract

We present a phenomenological model to investigate the chiral phase transition characterized by parity doubling in dense, beta equilibrated, cold matter. Our model incorporates effective interactions constrained by SU(3) relations and considers baryonic degrees of freedom. By constraining the model with astrophysical data and nuclear matter properties, we find a first-order phase transition within realistic values of the slope parameter L. The inclusion of the baryon octet and negative parity partners, along with a chiral-invariant mass $m_{0}$, allows for a non-massless chiral symmetric phase. Through exploration of parameter space, we identify parameter sets satisfying mass and radius constraints without requiring a partonic phase. The appearance of the parity partner of the nucleon, the N(1535) resonance, suppresses strangeness, pushing hyperonization to higher densities. We observe a mild first-order phase transition to the chirally restored phase, governed by $m_{0}$. Our calculations of surface tension highlight its strong dependence on $m_{0}$. The existence of mixed phases is ruled out since they become energetically too costly. We compare stars with metastable and stable cores using both branches of the equation of state. Despite limited lifespans due to low surface tension values, phase conversion and star contraction could impact neutron stars with masses around 1.3 solar masses or more. We discuss some applications of this model in its non-zero temperatures generalization and scenarios beyond beta equilibrium that can provide insights into core-collapse supernovae, proto-neutron star evolution, and neutron star mergers. Core-collapse supernovae dynamics, influenced by chiral symmetry restoration and exotic hadronic states, affect explosion mechanisms and nucleosynthesis.