Bayesian inference of the dense-matter equation of state of neutron stars with antikaon condensation
Vishal Parmar, Vivek Baruah Thapa, Anil Kumar, Debades Bandyopadhyay, Monika Sinha
Abstract
In this paper, we employ the density dependent relativistic hadron (DDRH) field theoretical model in a Bayesian analysis to investigate the equation of state (EOS) of dense matter featuring antikaon condensation for ${K}^{\ensuremath{-}}$ and ${\overline{K}}^{0}$ inside neutron stars. The vector coupling parameters within the kaonic sector are determined through the isospin counting rule and quark model. Our study integrates various constraints, including chiral effective field theory ($\ensuremath{\chi}\mathrm{EFT}$) calculations, nuclear saturation properties, and astrophysical observations from pulsars PSR $\mathrm{J}0030+0451$ and PSR $\mathrm{J}0740+66$ and from the GW170817 event. We present posterior distributions of model parameters derived from these constraints, enabling us to explore the distributions of nuclear matter properties and neutron star (NS) characteristics such as radii, tidal deformabilities, central energy densities, and speed of sound. The antikaon potential at the 68(90)% confidence intervals is determined to be $\ensuremath{-}129.{36}_{\ensuremath{-}3.837(\ensuremath{-}5.696)}^{+12.53(+32.617)}\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$. This aligns with several studies providing estimates within the range of $\ensuremath{-}120$ to $\ensuremath{-}150\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$. We find that the maximum neutron star mass is constrained to around $2{M}_{\ensuremath{\bigodot}}$ due to the significant softening of the EOS caused by antikaon condensation. This softening results in a considerable decrease in the speed of sound. Although antikaon condensation for ${K}^{\ensuremath{-}}$ is not feasible inside canonical neutron stars, it becomes feasible for higher NS masses. The condensation of both ${K}^{\ensuremath{-}}$ and ${\overline{K}}^{0}$ is probably present in the interior of neutron stars with mass greater than $2{M}_{\ensuremath{\bigodot}}$. We also discuss the interconnections among input variables, isoscalar and isovector aspects of the EOS, and specific NS properties in the context of antikaon condensation.