Viscosity bound and causality violation.
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.
Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Mauro
M
Brigante
Hong
H
Liu
Robert C
RC
Myers
Stephen
S
Shenker
Sho
S
Yaida