2019/02/28 by Gamal G. L. Nashed, Salvatore Capozziello
Physics and Astronomy · #gr-qc #astro-ph.HE #hep-th
paper · pdf · doi:10.1103/physrevd.99.104018
published as Phys. Rev. D 99, 104018 (2019) · 17 pages, 5 figures, accepted for publication in Physical Review D. This version contains an Addendum where a typo is pointed out. arXiv admin note: text overlap with arXiv:1107.3705 by other authors
arxiv created 2019/07/14 · arxiv updated 2019/07/18
A new class of analytic charged spherically symmetric black hole solutions, which behave asymptotically as flat or (A)dS spacetimes, is derived for specific classes of f(R) gravity, i.e., f(R)=R-2α√(R) and f(R)=R-2α√(R-8Λ), where Λ is the cosmological constant. These black holes are characterized by the dimensional parameter α that makes solutions deviate from the standard solutions of general relativity. The Kretschmann scalar and squared Ricci tensor are shown to depend on the parameter α which is not allowed to be zero. Thermodynamical quantities, like entropy, Hawking temperature, quasi-local energy and the Gibbs free energy are calculated. From these calculations, it is possible to put a constrain on the dimensional parameter α to have 0<α<0.5, so that all thermodynamical quantities have a physical meaning. The interesting result of these calculations is the possibility of a negative black hole entropy. Furthermore, present calculations show that for negative energy, particles inside a black hole, behave as if they have a negative entropy. This fact gives rise to instability for fRR<0. Finally, we study the linear metric perturbations of the derived black hole solution. We show that for the odd-type modes, our black hole is always stable and has a radial speed with fixed value equal to 1. We also, use the geodesic deviation to derive further stability conditions.