Hyperon effects in covariant density functional theory with recent astrophysical observations

TL;DR

This paper investigates how including strangeness-bearing hyperons in covariant density functional models affects neutron star properties, showing significant impacts on the equation of state and compatibility with recent astrophysical observations.

Contribution

It introduces the effects of $ ext{Λ}$-hyperons in covariant density functional theory using DDRHF and RMF, highlighting their influence on neutron star structure and observational consistency.

Findings

Hyperons soften the equation of state significantly.

DDRHF predicts reduced neutron star mass and radius.

Results align with observational data requiring small neutron star radii.

Abstract

Motivated by recent observational data, the equations of state with the inclusion of strangeness-bearing $\Lambda$-hyperons and the corresponding properties of neutron stars are studied, based on the covariant density functional (CDF) theory. To this end, we specifically employ the density dependent relativistic Hartree-Fock (DDRHF) theory and the relativistic mean field theory (RMF). The inclusion of $\Lambda$-hyperons in neutron stars shows substantial effects in softening the equation of state. Because of the extra suppression effect originated from the Fock channel, large reductions on both the star mass and radius are predicted by the DDRHF calculations. It is also found that the mass-radius relations of neutron stars with $\Lambda$-hyperons determined by DDRHF with the PKA1 parameter set are in fairly good agreement with the observational data where a relatively small neutron stars radius is required. Therefore, it is expected that the exotic degrees of freedom such as the strangeness-bearing structure may appear and play significant roles inside the neutron stars, which is supported further by the systematical investigations on the consistency between the maximum neutron star mass and $\Lambda$-coupling strength.