2007/04/30 by Kimmo Kainulainen, Johanna Piilonen, Vappu Reijonen +1 · 7 citations
Physics and Astronomy · #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #Solar and Space Plasma Dynamics #astro-ph #gr-qc #hep-th
paper · pdf · doi:10.1103/physrevd.76.024020
published as Phys.Rev.D76:024020,2007 · Published version, 12 pages, 7 figures
openalex publication_date 2007/07/31 · arxiv created 2008/03/07 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We study both analytically and numerically the gravitational fields of stars in f(R) gravity theories. We derive the generalized Tolman-Oppenheimer-Volkov equations for these theories and show that in metric f(R) models the parametrized post-Newtonian parameter \ensuremathγPPN=1/2 is a robust outcome for a large class of boundary conditions set at the center of the star. This result is also unchanged by the introduction of dark matter in the solar system. We find also a class of solutions with \ensuremathγPPN\ensuremath≈1 in the metric f(R)=R\ensuremath-\ensuremathμ4/R model, but these solutions turn out to be unstable and decay in time. On the other hand, the Palatini version of the theory is found to satisfy the solar system constraints. We also consider compact stars in the Palatini formalism, and show that these models are not inconsistent with polytropic equations of state. Finally, we comment on the equivalence between f(R) gravity and scalar-tensor theories and show that many interesting Palatini f(R) gravity models cannot be understood as a limiting case of a Jordan-Brans-Dicke theory with \ensuremathω\ensuremath→\ensuremath-3/2.