Examination of strangeness instabilities and effects of strange meson couplings in dense strange hadronic matter and compact stars

TL;DR

This study investigates the role of strange meson couplings in dense strange hadronic matter and neutron stars, finding no instabilities at supersaturation density within constrained models and highlighting the importance of hyperon interactions.

Contribution

The paper demonstrates that strangeness instabilities depend on hyperon interactions and shows that realistic neutron star properties can be achieved without such instabilities by constraining model parameters.

Findings

No supersaturation density instability in constrained RMF models.

Reasonable neutron star radii and masses with significant hyperon content.

Hyperon content is mainly governed by unconstrained strange meson couplings.

Abstract

Background : The emergence of hyperon degrees of freedom in neutron star matter has been associated to first order phase transitions in some phenomenological models, but conclusions on the possible physical existence of an instability in the strangeness sector are strongly model dependent. Purpose : The purpose of the present study is to assess whether strangeness instabilities are related to specific values of the largely unconstrained hyperon interactions, and to study the effect of the strange meson couplings on phenomenological properties of neutron stars and supernova matter, once these latter are fixed to fulfill the constraints imposed by hypernuclear data. Method : We consider a phenomenological RMF model sufficiently simple to allow a complete exploration of the parameter space. Results : We show that no instability at supersaturation density exists for the RMF model, as long as the parameter space is constrained by basic physical requirements. This is at variance with a non-relativistic functional, with a functional behavior fitted through ab-initio calculations. Once the study is extended to include the full octet, we show that the parameter space allows reasonable radii for canonical neutron stars as well as massive stars above two-solar mass, together with an important strangeness content of the order of 30\%, slightly decreasing with increasing entropy, even in the absence of a strangeness driven phase transition. Conclusions : We conclude that the hyperon content of neutron stars and supernova matter cannot be established with present constraints, and is essentially governed by the unconstrained coupling to the strange isoscalar meson.