Neutron stars in 4D Einstein-Gauss-Bonnet gravity

TL;DR

This paper investigates neutron star solutions in 4D Einstein-Gauss-Bonnet gravity, analyzing their stability and mass-radius relations using various equations of state, and finds that stability features resemble those in general relativity with notable modifications.

Contribution

It provides the first detailed analysis of radial perturbations and stability of neutron stars in 4D Einstein-Gauss-Bonnet gravity with multiple equations of state.

Findings

Stability and maximum mass points in 4DEGB resemble those in GR.

Larger coupling $oldsymbol{\alpha}$ increases neutron star mass at fixed radius.

Solutions approach stability near black hole solutions on the mass-radius diagram.

Abstract

Since the derivation of a well-defined $D\to4$ limit for 4D Einstein-Gauss-Bonnet (4DEGB) gravity coupled to a scalar field, there has been considerable interest in testing it as an alternative to Einstein's general theory of relativity. Past work has shown that this theory hosts interesting compact star solutions which are smaller in radius than a Schwarzschild black hole of the same mass in general relativity (GR), though the stability of such objects has been subject to question. In this paper we solve the equations for radial perturbations of neutron stars in the 4DEGB theory with Skyrme Lyon (SLy)/Brussels-Montreal Skyrme functionals (BSk) class equations of state (EOSs), along with the M\"uller-Serot (MS2) EOS, and show that the coincidence of stability and maximum mass points in GR is still present in this modified theory, with the interesting additional feature of solutions re-approaching stability near the black hole solution on the mass-radius diagram. Besides this, as expected from past work, we find that larger values of the 4DEGB coupling $\alpha$ tend to increase the mass of neutron stars of the same radius (due to a larger $\alpha$ weakening gravity) and move the maximum mass points of the solution branches closer to the black hole horizon.