Strange quark matter from a baryonic approach

TL;DR

This paper develops a baryonic model for dense matter that incorporates strangeness and chiral phase transitions, providing insights into the properties of matter in neutron stars and the nature of high-density QCD phases.

Contribution

It introduces a unified, simple model based on nuclear matter properties that captures chiral transitions, strangeness, and high-density behavior relevant for compact stars.

Findings

Chiral phase transition can be first order or crossover depending on parameters.

Strangeness does not appear as hyperons in the chirally broken phase within the allowed parameter range.

Reproducing massive compact stars constrains the model parameters, especially the symmetry energy slope.

Abstract

We construct a model for dense matter based on low-density nuclear matter properties that exhibits a chiral phase transition and that includes strangeness through hyperonic degrees of freedom. Empirical constraints from nuclear matter alone allow for various scenarios, from a strong first-order chiral transition at relatively low densities through a weaker transition at higher densities, even up to a smooth crossover not far beyond the edge of the allowed range. The model parameters can be chosen such that at asymptotically large densities the chirally restored phase contains strangeness and the speed of sound approaches the conformal limit, resulting in a high-density phase that resembles deconfined quark matter. Additionally, if the model is required to reproduce sufficiently massive compact stars, the allowed parameter range is significantly narrowed down, resulting for instance in a very narrow range for the poorly known slope parameter of the symmetry energy, $L\simeq (88-92)\, {\rm MeV}$. We also find that for the allowed parameter range strangeness does not appear in the form of hyperons in the chirally broken phase and the chiral transition is of first order. Due to its unified approach and relative simplicity - here we restrict ourselves to zero temperature and the mean-field approximation - the model can be used in the future to study dense matter under compact star conditions in the vicinity of the chiral phase transition, for instance to compute the surface tension or to investigate spatially inhomogeneous phases.