The viscosity bound in string theory Original Research Article

The ratio of shear viscosity to entropy density η/s of any material in nature has been conjectured to have a lower bound of 1/4π, the famous KSS bound. We examine string theory models for evidence in favour of and against this conjecture. We show that in a broad class of models quantum corrections yield values of η/s just above the KSS bound. However, incorporating matter fields in the fundamental representation typically leads to violations of this bound. We also outline a program to extend AdS/CFT methods to RHIC phenomenology.