Shedding Light on the EOS-Gravity Degeneracy and Constraining the Nuclear Symmetry Energy from the Gravitational Binding Energy of Neutron Stars

TL;DR

This paper explores how nuclear symmetry energy influences neutron star binding energy within general relativity and scalar-tensor gravity, aiming to help distinguish effects of dense matter physics from gravity theories.

Contribution

It analyzes the impact of nuclear symmetry energy parameters on neutron star binding energy in different gravity models, addressing the EOS-gravity degeneracy problem.

Findings

Variation in symmetry energy slope L significantly affects binding energy.

Differences between GR and scalar-tensor models are small for less massive stars.

High-density symmetry energy behavior also impacts neutron star properties.

Abstract

A thorough understanding of properties of neutron stars requires both a reliable knowledge of the equation of state (EOS) of super-dense nuclear matter and the strong-field gravity theories simultaneously. To provide information that may help break this EOS-gravity degeneracy, we investigate effects of nuclear symmetry energy on the gravitational binding energy of neutron stars within GR and the scalar-tensor subset of alternative gravity models. We focus on effects of the slope $L$ of nuclear symmetry energy at saturation density and the high-density behavior of nuclear symmetry energy. We find that the variation of either the density slope $L$ or the high-density behavior of nuclear symmetry energy leads to large changes in the binding energy of neutron stars. The difference in predictions using the GR and the scalar-tensor theory appears only for massive neutron stars, and even then is significantly smaller than the difference resulting from variations in the symmetry energy.