Brustein, R and Medved, A.J.M (2011) Nonperturbative unitarity constraints on the ratio of shear viscosity to entropy density in ultravioletcomplete theories with a gravity dual. Physical Review D, 84 (12). p. 126001. ISSN 15507998

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Abstract
We reconsider, from a novel perspective, how unitarity constrains the corrections to the ratio of shear viscosity η to entropy density s. We start with higherderivative extensions of Einstein gravity in asymptotically antide Sitter spacetimes. It is assumed that these theories are derived from string theory and thus have a unitary UV completion that is dual to a unitary, UVcomplete boundary gauge theory. We then propose that the gravitational perturbations about a solution of the UVcomplete theory are described by an effective theory whose linearized equations of motion have at most two time derivatives. Our proposal leads to a concrete prescription for the calculation of η/s for theories of gravity with arbitrary higherderivative corrections. The resulting ratio can take on values above or below 1/4π and is consistent with all the previous calculations, even though our reasoning is substantially different. For the purpose of calculating η/s, our proposal also leads to only two possible candidates for the effective twoderivative theory: Einstein and GaussBonnet gravity. The distinction between the two is that Einstein gravity satisfies the equivalence principle, and so its graviton correlation functions are polarizationindependent, whereas the GaussBonnet theory has polarizationdependent correlation functions. We discuss the graviton threepoint functions in this context and explain how these can provide additional information on the value of η/s.
Item Type:  Article 

Uncontrolled Keywords:  blackhole entropy; Noether charge; fieldtheories 
Subjects:  Q Science > QC Physics 
Divisions:  Faculty > Faculty of Science > Physics & Electronics 
ID Code:  2325 
Deposited By:  Mrs Eileen Shepherd 
Deposited On:  05 Jan 2012 14:11 
Last Modified:  06 Jan 2012 16:22 
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