Charged $\rho$-meson condensation in neutron stars

TL;DR

This paper explores the possibility of charged rho meson condensation in neutron star matter using extended relativistic mean-field models, analyzing its effects on the equation of state and neutron star properties.

Contribution

It introduces models incorporating rho meson condensation with hyperons and Delta baryons, examining the phase transition types and their impact on neutron star mass and composition.

Findings

Rho minus condensation can occur via second-order or first-order phase transitions.

The maximum neutron star mass is only slightly affected by rho minus condensation.

Matter composition undergoes significant rearrangement with rho minus condensation.

Abstract

We extend relativistic mean-field models with hadron masses and meson-baryon coupling constants dependent on the scalar field $\sigma$, including hyperons and $\Delta(1232)$ baryons, to incorporate a possibility of the charged $\rho$ meson condensation in neutron star matter. The influence of the $\rho^-$ condensation on the equation of state proves to be strongly model dependent. In our models of one type (KVORcut-based ones) the $\rho^-$ condensation arises by a second-order phase transition above a critical density and the maximum value of the neutron star mass diminishes only slightly. The matter composition changes more significantly. In our models of other type (MKVOR*-based ones), if the system is considered at fixed density, the $\rho^-$ condensation arises by a second-order phase transition at the baryon density $n=n_{c,\rho}^{(\rm II)}$ and at a slightly higher density $n=n_{c,\rho}^{(\rm I)}$ there occurs a first-order phase transition. In a neutron star matter starting with a density $n<n_{c,\rho}^{(\rm II)}$ there appears a region of a mixed phase, or the system is described by Maxwell construction, that results in a substantial decrease of the value of the maximum neutron star mass. Nevertheless in the models under consideration the observational constraint on the maximum neutron star mass is fulfilled. Besides, in MKVOR*-based models the appearance of the $\rho^-$ condensate is accompanied by a strong rearrangement of the matter composition. Dependence of the results on a choice of the $\rho$ meson scaling functions for the effective $\rho$ meson mass and coupling constants is also investigated.