Effects of isoscalar- and isovector-scalar meson mixing on neutron star structure

TL;DR

This paper investigates how mixing isoscalar and isovector scalar mesons in a relativistic mean field model affects neutron star properties, achieving compatibility with multiple astrophysical and nuclear experimental constraints.

Contribution

It introduces a modified RMF model with meson mixing that better aligns with diverse nuclear and astrophysical observations, resolving previous tensions.

Findings

The model softens symmetry energy at intermediate densities.

It stiffens symmetry energy at high densities.

The model agrees with neutron star mass and radius measurements.

Abstract

Based on the accurately calibrated interaction FSUGold, we show that including isovector scalar $\delta$ meson and its coupling to isoscalar scalar $\sigma$ meson in the relativistic mean field (RMF) model can soften the symmetry energy $E_{\rm{sym}}(n)$ at intermediate densities while stiffen the $E_{\rm{sym}}(n)$ at high densities. We find this new RMF model can be simultaneously compatible with (1) the constraints on the equation of state of symmetric nuclear matter at suprasaturation densities from flow data in heavy-ion collisions, (2) the neutron skin thickness of $^{208}$Pb from the PREX-II experiment, (3) the largest mass of neutron star (NS) reported so far from PSR J0740+6620, (4) the limit of $\Lambda_{1.4}\leq580$ for the dimensionless tidal deformability of the canonical 1.4$M_{\odot}$ NS from the gravitational wave signal GW170817, (5) the mass-radius relation of PSR J0030+0451 and PSR J0740+6620 measured by NICER, and thus remove the tension between PREX-II and GW170817 observed in the conventional RMF model.