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

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.

13 pages, 18 figures. References added. Discussion around Fig. 18 extended. Agrees with published version

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• Metric-affine effects in crystallization processes of white dwarfs
• The gravitational field of a star in quadratic gravity
• $R^2$-gravity quark stars from perturbative QCD
• Cooling Process of White Dwarf Stars in Palatini $f(R)$ Gravity
• Constraining fundamental parameters in modified gravity using Gaia-DR2 massive white dwarf observation