Beyond eta/s = 1/4pi

Abstract

We use low-energy effective description of gauge theory/string theory duality to argue that the Kovtun-Son-Starinets viscosity bound is generically violated in superconformal gauge theories with non-equal central charges $c\ne a$. We present new examples (of string theory constructions and of gauge theories) where the bound is violated in a controllable setting. We consider the comparison of results from AdS/CFT calculations to the QCD plasma in the context of this discussion.

44 pages, v2: Minor changes to numerics in section 4, references added, v3: published version

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• A bound on the speed of sound from holography
• Higher derivative effects on eta/s at finite chemical potential
• Higher Derivative Corrections to Shear Viscosity from Graviton's Effective Coupling
• Shear Viscosity to Entropy Density Ratio in Six Derivative Gravity
• Non-relativistic metrics with extremal limits
• R^2 Corrections to Asymptotically Lifshitz Spacetimes
• Non-relativistic D3-brane in the presence of higher derivative corrections
• Universal relations of transport coefficients from holography
• Strings on AdS Wormholes
• Robustness of Sound Speed and Jet Quenching for Gauge/Gravity Models of Hot QCD
• The Double Life of Thermal QCD
• Landscape versus Swampland for Higher Derivative Gravity
• Viscosity to entropy density ratio: violation of the lower bound at small temperatures