Hyperon Puzzle of Neutron Stars with Skyrme Force Models

TL;DR

This paper investigates the hyperon puzzle in neutron stars using Skyrme force models, exploring how hyperon interactions influence the maximum mass and radius, and identifying models consistent with recent observations of massive neutron stars.

Contribution

It introduces a comprehensive analysis of hyperon interactions within Skyrme models to reconcile neutron star mass observations with hyperon presence.

Findings

Certain Skyrme models predict neutron star maximum masses compatible with 2 solar masses.

Hyperon interactions can both soften and stiffen the EoS, affecting star mass and radius.

Some models satisfy observational constraints on mass and radius simultaneously.

Abstract

We consider the so called hyperon puzzle of neutron star (NS). We employ Skyrme force models for the description of in-medium nucleon-nucleon, nucleon-Lambda hyperon ($N\Lambda$), and Lambda-Lambda ($\Lambda\Lambda$) interactions. A phenomenological finite-range force for the $\Lambda\Lambda$ interaction is considered as well. Equation of state (EoS) of NS matter is obtained in the framework of density functional theory, and Tolman-Oppenheimer-Volkoff equations are solved to obtain the mass-radius relations of NSs. It has been generally known that the existence of hyperons in the NS matter is not well supported by the recent discovery of large-mass NSs ($M \simeq 2 M_\odot$) since hyperons make the EoS softer than the one without them. For the selected interaction models, $N\Lambda$ interactions reduce the maximum mass of NS by about 30~\%, while $\Lambda\Lambda$ interactions can give about 10~\% enhancement. Consequently, we find that some Skyrme force models predict the maximum mass of NS consistent with the observation of $2 M_\odot$ NSs, and at the same time satisfy observationally constrained mass-radius relations.