Dense matter equation of state of a massive neutron star with anti-kaon condensation

TL;DR

This study explores how anti-kaon condensation affects the dense matter equation of state in massive neutron stars, showing it can soften the EoS and influence maximum mass, with implications for exotic matter presence.

Contribution

It provides a detailed analysis of anti-kaon condensation effects on neutron star matter using covariant density functional theory, constrained by experimental data.

Findings

Anti-kaon condensation softens the equation of state.

A first-order phase transition can produce 2 solar mass neutron stars.

$ar{K}^0$ condensation occurs via second-order phase transition.

Abstract

Recent measurements of neutron star mass from several candidates (PSR J$1614-2230$, PSR J$0348+0432$, MSP J$0740+6620$) set the lower bound on the maximum possible mass for this class of compact objects $\sim 2$ M$_\odot$. Existence of stars with high mass brings the possibility of existence of exotic matter (hyperons, meson condensates) at the core region of the objects. In this work, we investigate the (anti)kaon ($K^-, \bar{K}^0$) condensation in $\beta-$equilibrated nuclear matter within the framework of covariant density functional theory. The functionals in the kaonic sector are constrained by the experimental studies on $K^-$ atomic, kaon-nucleon scattering data fits. We find that the equation of state softens with the inclusion of (anti)kaon condensates, which lowers the maximum mass of neutron star. In one of the density-independent coupling cases, the $K^-$ condensation is through a first-order phase transition type, which produces a $2$ M$_\odot$ neutron star. The first-order phase transition results in mixed phase region in the inner core of the stars. While $\bar{K}^0$ condensation appears via second-order phase transition for all the models we consider here.