Relativistic parameterizations of neutron matter and implications for neutron stars

TL;DR

This paper develops relativistic mean-field models for neutron matter constrained by recent data, analyzing their physical validity and implications for neutron star properties, including mass, radius, and tidal deformability.

Contribution

It introduces new parameter sets fitted to recent constraints, examines their physical behavior, and explores implications for neutron star structure and observational data.

Findings

Unphysical behavior appears in stiff models with low effective mass.

Neutron star maximum mass exceeds 2 solar masses across acceptable models.

Neutron star radius at 1.4 solar masses is nearly independent of the slope parameter L.

Abstract

We construct parameter sets of the relativistic mean-field model fitted to the recent constraints on the asymmetry energy $J$ and the slope parameter $L$ for pure neutron matter. We find cases of unphysical behaviour, i.e.\ the appearance of negative pressures, for stiff parameter sets with low values of the effective mass $m^*/m$. In some cases the equation of state of pure neutron matter turns out to be outside the allowed band given by chiral effective field theory. The mass-radius relations of neutron stars for all acceptable parameter sets shows a maximum mass in excess of $2M_\odot$ being compatible with pulsar mass measurements. Given the constraints on the model in the low-density regime coming from chiral effective theory, we find that the radius of a $1.4M_\odot$ neutron star is nearly independent on the value of $L$. This is in contrast to some previous claims for a strong connection of the slope parameter with the radius of a neutron star. In fact, the mass-radius relation turns out to depend only on the isoscalar parameters of symmetric matter. The constraints of GW170817 on the tidal deformability and on the radius are also discussed.