2008/08/26 by Ram Brustein, A. J. M. Medved · 1 citation
Physics and Astronomy · #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #Galaxies: Formation, Evolution, Phenomena #hep-th
paper · pdf · doi:10.1103/physrevd.79.021901
published as Phys.Rev.D79:021901,2009 · 11 pages
arxiv created 2008/08/26 · openalex publication_date 2009/01/14 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Near the horizon of a black brane solution in anti-de Sitter space, the long-wavelength fluctuations of the metric exhibit hydrodynamic behavior. For Einstein's theory, the ratio of the shear viscosity of near-horizon metric fluctuations \ensuremathη to the entropy per unit of transverse volume s is \ensuremathη/s=1/4\ensuremathπ. We propose that, in generalized theories of gravity, this ratio is given by the ratio of two effective gravitational couplings and can be different than 1/4\ensuremathπ. Our proposal confirms that \ensuremathη/s is equal to 1/4\ensuremathπ for any theory that can be transformed into Einstein's theory, such as F(R) gravity. Our proposal also implies that matter interactions---except those including explicit or implicit factors of the Riemann tensor---will not modify \ensuremathη/s. The proposed formula reproduces, in a very simple manner, some recently found results for Gauss-Bonnet gravity. We also make a prediction for \ensuremathη/s in Lovelock theories of any order or dimensionality.