S-wave kaon condensation in neutron-star matter within a chiral model framework with dynamical meson masses

TL;DR

This paper models s-wave kaon condensation in neutron-star matter using an advanced chiral mean field framework with dynamical meson masses, analyzing its effects on the equation of state and neutron-star properties.

Contribution

It introduces a self-consistent chiral model with dynamical meson masses to study kaon condensation and its impact on neutron-star matter, improving upon previous constant-mass approaches.

Findings

Kaon condensation occurs between 2-8 times nuclear saturation density.

Kaon condensation influences the neutron-star equation of state and cooling.

Results are compatible with observed 2-solar-mass neutron stars.

Abstract

We investigate s-wave kaon condensation in dense matter and neutron stars within the updated Chiral Mean Field model with an improved meson description (mCMF), which incorporates dynamically generated in-medium meson masses arising from explicit chiral symmetry breaking and vector-meson self-interactions. In contrast to conventional relativistic mean-field descriptions with constant meson masses, the mCMF framework introduces a self-consistent feedback between the meson sector and the dense-matter equations of motion. The kaon dispersion relation is derived from the nonlinear SU(3) Lagrangian, including the Weinberg-Tomozawa interaction and additional baryon-pseudoscalar couplings, and the onset of condensation is determined under conditions of charge neutrality and $\beta$ equilibrium. Our calculations include the full baryon octet together with electrons and muons at zero temperature. We analyze the impact of hyperons, muons, and kaon condensation on the equation of state, on neutron-star mass--radius relations, and neutron-star thermal evolution, and examine the sensitivity of the onset density and stellar properties to variations in the nucleon--kaon scattering length and to different model vector parameters and vector self-interactions. We find that $K^{-}$ condensation sets in between $n \sim (2-8)\, n_0$ (in units of nuclear saturation density) and leads to a moderate to strong softening (in one case, a slight stiffening of the equation of state), depending on the interplay of kaons and hyperons, while remaining compatible with current $2\,M_\odot$ and small-radius neutron-star observational constraints and producing distinguishable behavior in the neutron-star cooling. This work provides an improved and thermodynamically consistent framework for studying exotic degrees of freedom in neutron-star matter.