The ratio of shear viscosity to entropy density in generalized theories of gravity

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dc.creatorBrustein, Ram
dc.creatorMedved, A. J. M.
dc.date2008-08-26
dc.date.accessioned2026-07-07T12:31:48Z
dc.date.available2026-07-07T12:31:48Z
dc.descriptionNear the horizon of a black brane solution in Anti-de Sitter space, the long-wavelength fluctuations of the metric exhibit hydrodynamic behaviour. For Einstein's theory, the ratio of the shear viscosity of near-horizon metric fluctuations eta to the entropy per unit of transverse volume s is eta/s=1/4 pi. 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 pi. Our proposal implies that eta/s is equal for any pair of gravity theories that can be transformed into each other by a field redefinition. In particular, the ratio is 1/4 pi 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 eta/s. The proposed formula reproduces, in a very simple manner, some recently found results for Gauss-Bonnet gravity. We also make a prediction for eta/s in Lovelock theories of any order or dimensionality.
dc.description11 pages
dc.identifierhttps://arxiv.org/abs/0808.3498
dc.identifierhttp://arxiv.org/abs/0808.3498
dc.identifierPhys.Rev.D79:021901,2009
dc.identifierdoi:10.1103/PhysRevD.79.021901
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/216572
dc.subjectHigh Energy Physics - Theory
dc.titleThe ratio of shear viscosity to entropy density in generalized theories of gravity
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