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Viscosity Bound and Causality Violation

2008; American Physical Society; Volume: 100; Issue: 19 Linguagem: Inglês

10.1103/physrevlett.100.191601

1092-0145

Mauro Brigante, Hong Liu, Robert C. Myers, Stephen H. Shenker, Sho Yaida,

Noncommutative and Quantum Gravity Theories

In recent work we showed that, for a class of conformal field theories (CFT) with Gauss-Bonnet gravity dual, the shear viscosity to entropy density ratio, eta/s, could violate the conjectured Kovtun-Starinets-Son viscosity bound, eta/s > or = 1/4 pi. In this Letter we argue, in the context of the same model, that tuning eta/s below (16/25)(1/4 pi) induces microcausality violation in the CFT, rendering the theory inconsistent. This is a concrete example in which inconsistency of a theory and a lower bound on viscosity are correlated, supporting the idea of a possible universal lower bound on eta/s for all consistent theories.