Constraints on the curvature of nuclear symmetry energy from recent astronomical data within the KIDS framework

Abstract

In this paper, we investigate the density dependence of the nuclear symmetry energy [Formula: see text] in the KIDS (Korea-IBS-Daegu-SKKU) framework for the nuclear equation of state (EoS) and energy-density functional (EDF). The aim is to constrain the value of the curvature parameter ([Formula: see text]) based on recent astronomical data. First, assuming a standard saturation point, we calculate bulk nuclear properties within KIDS-EDF for different values of the compression modulus of symmetric nuclear matter ([Formula: see text]) and of the leading-order symmetry energy parameters, i.e., the symmetry energy ([Formula: see text]) and slope ([Formula: see text]) at saturation density, each within a broadly accepted range, as well as [Formula: see text]. All of the above EoS parameters are varied independently of each other. The skewness parameter ([Formula: see text]) is presently kept fixed at 650[Formula: see text]MeV. For all EoS parameter sets which describe the selected nuclear data within better than [Formula: see text], we calculate the neutron star EoS and mass–radius relation and analyze the results in terms of Pearson correlation coefficients [Formula: see text]. We find that the value of [Formula: see text] is strongly correlated with the radius of both a canonical and a massive star [Formula: see text]. If we impose that all known astronomical constraints on the neutron star radii must be satisfied, we deduce [Formula: see text]. As a result, the symmetry energy as a function of the density is consistently found to have an inflection point at [Formula: see text]. We take the opportunity to report that the neutron skin thickness of [Formula: see text]Pb shows no correlation at all with the neutron star radii [Formula: see text], in contrast with studies which focus on the role of [Formula: see text] only.