Black Holes, Entropy Bound and Causality Violation

Abstract

The gravity/gauge theory duality has provided us a way of studying QCD at short distances from straightforward calculations in classical general relativity. Among numerous results obtained so far, one of the most striking is the universality of the ratio of the shear viscosity to the entropy density. For all gauge theories with Einstein gravity dual, this ratio is η/s=1/4π. However, in general higher-curvature gravity theories, including two concrete models under discussion - the Gauss-Bonnet gravity and the (Riemann)^2 gravity - the ratio η/s can be smaller than 1/4π(thus violating the conjecture bound), equal to 1/4πor even larger than 1/4π. As we probe spacetime at shorter distances, there arises an internal inconsistency in the theory, such as a violation of microcausality, which is correlated with a classical limit on black hole entropy.

8 pages, no figures; Invited contribution to appear in the Proceedings of the 75 Years since Solvay, Singapore, Nov 2008, (World Scientific, Singapore, 2009)

References in corpus (1)

• Shear Viscosity from Effective Couplings of Gravitons

Cited by in corpus (12)

• Causality constraints in AdS/CFT from conformal collider physics and Gauss-Bonnet gravity
• Causality in AdS/CFT and Lovelock theory
• On Charged Lifshitz Black Holes
• Shear viscosity and instability from third order Lovelock gravity
• A Lovelock black hole bestiary
• Bounding the Temperatures of Black Holes Dual to Strongly Coupled Field Theories on Flat Spacetime
• R^2 Corrections to Asymptotically Lifshitz Spacetimes
• Moduli and electromagnetic black brane holography
• Viscosity bound for anisotropic superfluids in higher derivative gravity
• Holographic Consistency and the Sign of the Gauss-Bonnet Parameter
• $\eta /s$ at finite coupling
• Holographic RG flows and transport coefficients in Einstein-Gauss-Bonnet-Maxwell theory