Compact Stars in R-Squared Gravity

Abstract

Recent progress in testing certain modified-gravity theories has been achieved by the study of the structure of compact objects like Black Holes and Neutron Stars (NSs). In particular, it is possible that the squared-gravity generalization of the Lagrangian density, given by the function f(R)=R+α R^2, may yield acceptable models for heavier NSs than General Relativity (GR) does. In the strong gravitational regime, the differences among alternative gravity theories should be enhanced. Because of the complexity of the field equations, perturbative methods are required to approach solutions. In this work, we calculate the structure of both NSs and Quark Stars (QSs) focusing on the behaviour of their interior profiles, compared to those from GR. We find that these profiles depend on high-order derivatives of the Equations of State (EoSs), showing regions where the enclosed mass decreases with the radius in a counter-intuitive way.