Effective interactions of hyperons and mass-radius relation of neutron stars

TL;DR

This paper investigates how hyperons influence neutron star properties using a relativistic mean field model, showing that certain mesons can stiffen the equation of state and align with observed mass-radius constraints.

Contribution

It introduces a model incorporating hyperons and mesons that can produce realistic neutron star masses and radii, extending previous models to higher densities with constrained parameters.

Findings

Hyperons soften the equation of state at high densities.

The $ ext{phi}$ meson induces repulsion, stiffening the EOS.

Model predicts maximum neutron star mass consistent with observations.

Abstract

We examine the role of hyperons in a neutron star based on the relativistic mean field approach. For nuclear matter below 1.5 times the normal nuclear density we constrain the model parameters by using the symmetric nuclear matter properties and theoretical investigations for neutron matter in the literature. We then extend the model to higher densities by including hyperons and isoscalar vector mesons that contain strangeness degree of freedom. We confirm that the $\phi$ meson induces a $\Lambda$ repulsive force and hardens the equation of state. The hardening arising from the $\phi$ meson compensates the softening from the existence of hyperons. The flavor SU(3) and spin-flavor SU(6) relations are examined as well. We found that the coupling constants fitted by neutron matter properties could yield high enough maximum mass of a neutron star and the obtained results satisfy both the mass and radius constraints. The onset of the hyperon direct Urca process in neutron stars is also investigated using our parametrization.