Constraining compact star properties with nuclear saturation parameters

Abstract

A set of hadronic equations of state (EoSs) derived from relativistic density functional theory and constrained by terrestrial experiments, astrophysical observations, in particular by the GW170817 event, and chiral effective field theory ($\chi$EFT) of neutron matter is used to explore the sensitivity of the EoS parameterization on the few nuclear matter characteristics defined at the saturation density. We find that the gross properties of compact stars are most sensitive to the isoscalar skewness coefficient $Q_{\text{sat}}$ and the isovector slope coefficient $L_{\text{sym}}$ around saturation density, since the higher order coefficients, such as $K_{\text{sym}}$, are fixed by our model. More specifically, (i) among these $Q_{\text{sat}}$ is the dominant parameter controlling both the maximum mass and the radii of compact stars while $L_{\rm sym}$ is constrained somewhat by $\chi$EFT of neutron matter; (ii) massive enough ($M\sim 2.0~M_{\odot})$ compact stars featuring both hyperons and $\Delta$ resonances can be obtained if the value of $Q_{\text{sat}}$ is large enough; (iii) the emergence of $\Delta$'s reduces the radius of a canonical mass ($M\sim 1.4~M_{\odot})$ compact star thus easing the tension between the predictions of the relativistic density functionals and the inferences from the X-ray observation of nearby isolated neutron stars.