Impact of hyperons on structural properties of neutron stars and hybrid stars within the regularized four-dimensional Einstein-Gauss-Bonnet gravity

TL;DR

This study explores how hyperons and quark matter phase transitions influence neutron star properties within a modified gravity framework, showing that the Gauss-Bonnet coupling constant significantly affects star mass and radius predictions.

Contribution

It introduces a comprehensive analysis of hyperons and phase transitions in neutron stars within 4D Einstein-Gauss-Bonnet gravity, linking gravitational modifications to observable stellar properties.

Findings

Positive Gauss-Bonnet coupling supports 2 solar mass stars.

Negative coupling results in lower maximum masses, inconsistent with observations.

Hyperons and phase transitions soften the EoS, affecting star structure.

Abstract

We investigate the impact of hyperons and phase transition to quark matter on the structural properties of neutron stars within the regularized four-dimensional Einstein-Gauss-Bonnet gravity (4DEGB). We employ the density-dependent relativistic mean-field model (DDME2) for the hadronic phase and the density-dependent quark mass (DDQM) model for the quark phase to construct hadronic and hybrid equations-of-state (EoSs) that are consistent with the astrophysical constraints. The presence of hyperons softens the EoS and with a phase transition, the EoS further softens, and the speed of sound squared drops to around 0.2 for the maximum mass configuration, which lies in the pure quark phase. Adjusting the Gauss-Bonnet coupling constant, $\alpha$, within its allowed range results in a decrease in the mass-radius relationship for negative $\alpha$, and an increase for positive $\alpha$. In addition, functions are fitted to the maximum mass and its associated radius as a function of the constant $\alpha$ to observe its impact on these properties. We find that positive values of $\alpha$ support massive stars consistent with the 2\,$M_{\odot}$ constraint and NICER measurements, while negative values, although compatible with low-mass radius observations, fail to reach the observed maximum mass, particularly for EoSs involving phase transitions. Therefore, astrophysical observations may be used to effectively constrain the allowed range of $\alpha$.