69 research outputs found
The shear viscosity of holographic superfluids
We study the ratio of the shear viscosity to the entropy density for various
holographic superfluids. For the s-wave case, the ratio has the universal value
1/(4pi) as in various holographic models. For the p-wave case, there are two
shear viscosity coefficients because of the anisotropic boundary spacetime, and
one coefficient has the universal value. For the (p+ip)-wave case, the existing
technique is not applicable since there is no tensor mode of metric
perturbations which decouples from Yang-Mills perturbations. Our results
indicate that the shear viscosity does not show a singular behavior at the
critical point for holographic superfluids.Comment: 22 pages, PTPTe
Causal hydrodynamics and the membrane paradigm
We obtain the relaxation time for the shear viscous stress for various
geometries using the "membrane paradigm" formula proposed recently. We consider
the generic Schwarzschild-AdS black holes (SAdS), the generic Dp-brane, the
Klebanov-Tseytlin (KT) geometry, and the N=2* theory. The formula is the "shear
mode" result and is not fully trustable, but it may be helpful to learn some
generic behaviors about the relaxation time. For example, a simple formula
summarizes all known results for SAdS, and a single expression summarizes the
results for the Dp-brane and the KT geometry.Comment: 8 pages, ReVTeX
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