Structure of neutron stars in R-squared gravity. (arXiv:1301.5189v1 [astro-ph.CO])

Structure of neutron stars in R-squared gravity. (arXiv:1301.5189v1 [astro-ph.CO]):
The effects implied for the structure of compact objects by the modification
of General Relativity produced by the generalization of the Lagrangian density
to the form f(R)=R+\alpha R^2, where R is the Ricci curvature scalar, have been
recently explored. It seems likely that this squared-gravity may allow heavier
Neutron Stars (NSs) than GR. In addition, these objects can be useful to
constrain free parameters of modified-gravity theories. The differences between
alternative gravity theories is enhanced in the strong gravitational regime. In
this regime, because of the complexity of the field equations, perturbative
methods become a good choice to treat the problem. Following previous works in
the field, we performed a numerical integration of the structure equations that
describe NSs in f(R)-gravity, recovering their mass-radius relations, but
focusing on particular features that arise from this approach in the profiles
of the NS interior.

We show that these profiles run in correlation with the second-order
derivative of the analytic approximation to the Equation of State (EoS), which
leads to regions where the enclosed mass decreases with the radius in a
counter-intuitive way. We reproduce all computations with a simple polytropic
EoS to separate zeroth-order modified gravity effects.