Cemsinan Deliduman, K. Y. Ekşi, Vildan Keleş
We study the structure of neutron stars in R+\beta R^{\mu \nu} R_{\mu \nu} gravity model with perturbative method. We obtain mass-radius relations for six representative equations of state (EoSs). We find that deviations from the results of general relativity, comparable to the variations due to using different EoSs, are induced for |\beta| ~ 10^11 cm^2. Some of the soft EoSs that are excluded within the framework of general relativity can be reconciled for certain values of \beta\ of this order with the 2 solar mass neutron star recently observed. For some of the EoSs we find that a new solution branch, which allows highly massive neutron stars, exists for values of \beta\ greater than a few 10^11 cm^2. We find constraints on \beta\ for a variety of EoSs using the recent observational constraints on the mass-radius relation. The associated length scale \sqrt{\beta} ~ 10^6 cm is of the order of the the typical radius of neutron stars, the probe used in this test. This implies that the true value of \beta\ is most likely much smaller than 10^11 cm^2.
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http://arxiv.org/abs/1112.4154
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