Quarkyonic matter with strangeness in an extended RMF model

TL;DR

This paper develops a comprehensive relativistic mean field model to describe quarkyonic matter with strangeness, analyzing its impact on neutron star properties and the equation of state at high densities.

Contribution

It introduces a unified framework for quarkyonic matter with strangeness, including hyperons and strange quarks, and explores their effects on neutron star equations of state.

Findings

Hyperons soften the equation of state and reduce neutron star masses and radii.

The equation of state exhibits a maximum sound velocity near 0.6c, consistent with observations.

Inclusion of quark-hadron phase transition further softens the EoS at high densities.

Abstract

Quarkyonic matter is expected to play a key role for the transition from hadronic matter to quark matter in compact stars. Within the framework of the relativistic mean field (RMF) model and equivparticle model with density-dependent quark masses, we construct the ``quark Fermi sea" with a ``baryon Fermi surface" to characterize the properties of the quarkyonic matter. In particular, we develop a comprehensive framework to account for the strangeness degrees of freedom, incorporating $\Lambda$, $\Xi$, and $\Sigma$ hyperons as well as strange quarks in a unified quarkyonic framework. Our calculations indicate that the inevitable emergence of hyperons softens the equations of state, leading to a reduction in the speed of sound around $n_{\rm b}\approx 2n_0$, and consequently reducing the masses and radii of neutron stars. When the quark-hadron phase transition is taken into account, the equation of state at high densities exhibits additional softening, leading to a maximum sound velocity of $v_{\rm max} \approx 0.6\,c$, which is close to the ultrarelativistic limit of $0.58\,c$, consistent with current astronomical observational constraints.