Massradius relation for neutron stars in f (R ) gravity
Abstract
We discuss the massradius diagram for static neutron star models obtained by the numerical solution of modified TolmanOppenheimerVolkoff equations in f (R ) gravity where the Lagrangians f (R )=R +α R^{2}(1 +γ R ) and f (R )=R^{1 +∊} are adopted. Unlike the case of the perturbative approach previously reported, the solutions are constrained by the presence of an extra degree of freedom, coming from the trace of the field equations. In particular, the stiffness of the equation of state determines an upper limit on the central density ρ_{c} above which the positivity condition of energymatter tensor trace T^{m}=ρ 3 p holds. In the case of quadratic f (R ) gravity, we find higher masses and radii at lower central densities with an inversion of the behavior around a pivoting ρ_{c} which depends on the choice of the equation of state. When considering the cubic corrections, we find solutions converging to the required asymptotic behavior of the flat metric only for γ <0 . A similar analysis is performed for f (R )=R^{1 +∊} considering ∊ as the leading parameter. We work strictly in the Jordan frame in order to consider matter minimally coupled with respect to geometry. This fact allows us to avoid ambiguities that could emerge in adopting the Einstein frame.
 Publication:

Physical Review D
 Pub Date:
 January 2016
 DOI:
 10.1103/PhysRevD.93.023501
 arXiv:
 arXiv:1509.04163
 Bibcode:
 2016PhRvD..93b3501C
 Keywords:

 General Relativity and Quantum Cosmology;
 Astrophysics  High Energy Astrophysical Phenomena;
 High Energy Physics  Theory
 EPrint:
 10 pages, 6 figures, to appear in Phys. Rev. D