Neutron Stars in Palatini $R+\alpha R^2$ and $R+\alpha R^2+\beta Q$ Theories

TL;DR

This paper investigates how modifications to general relativity in Palatini $f(R)$ and $f(R,Q)$ theories affect neutron star properties, highlighting potential observational signatures for testing gravity theories.

Contribution

It provides a detailed analysis of neutron star solutions in Palatini $f(R)$ and $f(R,Q)$ theories, exploring the impact of quadratic curvature terms with various equations of state.

Findings

Modifications can significantly alter neutron star mass-radius relations.

Certain parameter combinations produce observable differences from GR predictions.

Astrophysical data could help constrain or detect deviations from general relativity.

Abstract

We study solutions of the stellar structure equations for spherically symmetric objects in Palatini $f(R)=R+\alpha R^2$ and $f(R,Q)=R+\alpha R^2+\beta Q$ in the mass-radius region associated to neutron stars. We illustrate the potential impact of the $R^2$ and $Q$ terms by studying a range of viable values of $\alpha$ and $\beta$. Similarly, we use different equations of state (SLy, FPS, HS(DD2) and HS(TMA)) as a simple way to account for the equation of state uncertainty. Our results show that for certain combinations of the $\alpha$ and $\beta$ parameters and equation of state, the effect of modifications of general relativity on the properties of stars is sizeable. Therefore, with increasing accuracy in the determination of the equation of state for neutron stars, astrophysical observations may serve as discriminators of modifications of General Relativity.