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

In this paper, we investigate the density dependence of the nuclear symmetry energy S(rho) 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 (K-sym) 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 (K-0) and of the leading-order symmetry energy parameters, i.e., the symmetry energy (J) and slope (L) at saturation density, each within a broadly accepted range, as well as All of the above EoS parameters are varied independently of each other. The skewness parameter (Q(sym)) is presently kept fixed at 650 MeV. For all EoS parameter sets which describe the selected nuclear data within better than 0.3%, we calculate the neutron star EoS and mass-radius relation and analyze the results in terms of Pearson correlation coefficients r. We find that the value of K(sym )is strongly correlated with the radius of both a canonical and a massive star (vertical bar r vertical bar > 0.9). If we impose that all known astronomical constraints on the neutron star radii must be satisfied, we deduce -150 < K-sym < 0. As a result, the symmetry energy as a function of the density is consistently found to have an inflection point at rho(o) < rho < 2 rho(0). We take the opportunity to report that the neutron skin thickness of Pb-208 shows no correlation at all with the neutron star radii (vertical bar r vertical bar < 0.1), in contrast with studies which focus on the role of L only.

Automated summary

In this paper, the density dependence of the nuclear symmetry energy is investigated in the framework of KIDS for the nuclear equation of state and energy-density functional. The aim is to constrain the value of the curvature parameter based on recent astronomical data. The results suggest that the symmetry energy has an inflection point within a certain density range.