Constraining Palatini gravity with GR-independent equations of state for neutron stars

TL;DR

This paper develops theory-based, GR-independent equations of state for neutron stars using fundamental principles, and uses them to constrain quadratic Palatini gravity parameters.

Contribution

It introduces a novel method to construct equations of state independent of General Relativity, based on first principles like chiral perturbation theory and QCD.

Findings

Constrained quadratic Palatini $f( ext{R})$ gravity parameter to $-6.47 ext{ km}^2 \

Indicated the importance of theory-based equations of state over astrophysical observables.

Discussed implications of phase transitions and twin stars in neutron star modeling.

Abstract

We demonstrate how to construct GR-independent equations of state. We emphasize the importance of using theory-based principles instead of relying solely on astrophysical observables and General Relativity (GR). We build a set of equations of state based on first principles, including chiral perturbation theory and perturbation theory in quantum chromodynamics. Interpolation methods are employed to assume thermodynamic stability and causality in the intermediate region. These equations of state are then used to constrain quadratic Palatini $f(\mathcal R)$ gravity, indicating that the parameter lies within the range $-6.47 \lesssim \beta \lesssim 1.99$ km$^2$. Additionally, we briefly discuss the problem of phase transitions and twin stars.