Nuclear Physics Seminar

Kovtun, Son and Starinets (KSS) motivated by elegant result on transport properties from AdS/CFT conjectured that the ratio of the viscosity always exceeds 1/(4 pi) for all fluids. This talk explores the robustness of this KSS conjecture. It is shown that from a theoretical perspective it is easy to construct models consistent with nonrelativistic quantum mechanics which violate the putative KSS bound. However, the models appear to be rather unrealistic in that they require an exponentially large number of species of constituent in the fluid. This raises the question of whether there is a deep principle beyond quantum mechanics which prevents the realization of such models and protects the KSS bound. One possible idea is that the underlying structure of quantum field theory might do this: it is conceivable that no consistent quantum field theory can reduce to a KSS violating nonrelativistic model. However, by considering a gas of heavy mesons in a rather special limit of generalized QCD, it is shown that consistent quantum field theories can yield systems which do violate the KSS bound---at least for the metastable fluids.