Slowly rotating neutron and strange stars in $R^2$ gravity

TL;DR

This paper models slowly rotating neutron and strange stars within $R^2$ gravity, deriving structure equations, solving for different equations of state, and showing that the moment of inertia can significantly differ from general relativity, aiding tests of gravity theories.

Contribution

It provides a self-consistent framework for analyzing slowly rotating stars in $f(R)$ gravity, including equations and solutions for various equations of state, highlighting observable differences from GR.

Findings

Neutron star moment of inertia can be up to 30% larger in $R^2$ gravity.

The change in moment of inertia exceeds EOS uncertainties.

Future measurements could distinguish $f(R)$ gravity from general relativity.

Abstract

In the present paper we investigate self-consistently slowly rotating neutron and strange stars in R-squared gravity. For this purpose we first derive the equations describing the structure of the slowly rotating compact stars in $f(R)$-gravity and then simultaneously solve the exterior and the interior problem. The structure of the slowly rotating neutron stars is studied for two different hadronic equations of state and a strange matter equation of state. The moment of inertia and its dependence on the stellar mass and the $R$-squared gravity parameter $a$ is also examined in details. We find that the neutron star moment of inertia for large values of the parameter $a$ can be up to $30\%$ larger compared to the corresponding general relativistic models. This is much higher than the change in the maximum mass induced by $R$-squared gravity and is beyond the EOS uncertainty. In this way the future observations of the moment of inertia of compact stars could allow us to distinguish between general relativity and $f(R)$ gravity, and more generally to test the strong field regime of gravity.