Possibility of s-wave pion condensates in neutron stars revisited

TL;DR

This paper investigates the potential for s-wave pion condensation in neutron stars using optical potentials and RMF models, concluding it is unlikely under typical conditions, especially with hyperons present.

Contribution

It provides a comprehensive re-evaluation of s-wave pion condensation possibilities in neutron stars using updated optical potentials and RMF models.

Findings

S-wave pion condensation is unlikely in neutron stars.

Hyperons suppress the possibility of pion condensation.

Density dependence of the b_1 parameter affects condensation likelihood.

Abstract

We examine possibilities of pion condensation with zero momentum (s-wave condensation) in neutron stars by using the pion-nucleus optical potential U and the relativistic mean field (RMF) models. We use low-density phenomenological optical potentials parameterized to fit deeply bound pionic atoms or pion-nucleus elastic scatterings. Proton fraction (Y_p) and electron chemical potential (mu_e) in neutron star matter are evaluated in RMF models. We find that the s-wave pion condensation hardly takes place in neutron stars and especially has no chance if hyperons appear in neutron star matter and/or b_1 parameter in U has density dependence.