Constraining the nuclear equation of state from terrestrial experiments and neutron star observations using relativistic mean-field models

TL;DR

This paper develops and tests new relativistic mean-field models of the nuclear equation of state, constrained by nuclear experiments and neutron star observations, revealing the importance of the curvature parameter in EoS behavior.

Contribution

Introduction of the OMEG family of RMF interactions with sigma-delta and omega-rho mixing, optimized to match terrestrial and astrophysical data.

Findings

The models can produce small neutron-star radii and tidal deformabilities.

Astrophysical data favor small or negative curvature parameter $K_{sym}$.

The sigma-delta mixing softens the symmetry energy at twice saturation density.

Abstract

We investigate the nuclear equation of state (EoS) for isospin-asymmetric matter using a new set of RMF interactions with the $\sigma$-$\delta$ and $\omega$-$\rho$ mixing, referred to as the OMEG family. These interactions are optimized so as to reproduce both terrestrial nuclear measurements and astrophysical constraints extracted from NICER and GW170817. The $\sigma$-$\delta$ mixing softens the nuclear symmetry energy and pressure around twice the saturation density, which enables relatively small neutron-star radii and tidal deformabilities while keeping the nuclear EoS sufficiently stiff at high densities to support $2M_{\odot}$ neutron stars. We find that the curvature parameter, $K_{\textrm{sym}}$, plays an important role in realizing the soft-to-hard behavior of the nuclear EoS, and the astrophysical data favor small or even negative values of $K_{\textrm{sym}}$.