Asymmetric nuclear matter in relativistic mean-field models with isoscalar- and isovector-meson mixing

TL;DR

This paper investigates how isoscalar and isovector meson mixing in relativistic mean-field models affects the properties of asymmetric nuclear matter and neutron stars, including symmetry energy, radius, and tidal deformability.

Contribution

It introduces a combined analysis of vector and scalar meson mixing effects on nuclear matter and neutron star properties within a relativistic mean-field framework.

Findings

The delta meson increases symmetry energy at high densities.

Sigma-delta mixing softens the symmetry energy above saturation density.

The model reproduces observed neutron star tidal deformabilities from GW170817 and GW190814.

Abstract

Using the relativistic mean-field model with nonlinear couplings between the isoscalar and isovector mesons, we study the properties of isospin-asymmetric nuclear matter. Not only the vector mixing, $\omega_{\mu}\omega^{\mu}\mathbf{\rho}_{\nu}\mathbf{\rho}^{\nu}$, but also the quartic interaction due to the scalar mesons, $\sigma^{2}\mathbf{\delta}^{2}$, is taken into account to investigate the density dependence of nuclear symmetry energy, $E_{\rm sym}$, and the neutron-star properties. It is found that the $\delta$ meson increases $E_{\rm sym}$ at high densities, whereas the $\sigma$-$\delta$ mixing makes $E_{\rm sym}$ soft above the saturation density. Furthermore, the $\delta$ meson and its mixing have a large influence on the radius and tidal deformability of a neutron star. In particular, the $\sigma$-$\delta$ mixing reduces the neutron-star radius, and, thus, the present calculation can simultaneously reproduce the dimensionless tidal deformabilities of a canonical $1.4M_{\odot}$ neutron star observed from the binary neutron star merger, GW170817, and from the compact binary coalescence, GW190814.