Is There a “Most Perfect Fluid” Consistent with Quantum Field Theory?

It was recently conjectured that the ratio of the shear viscosity to entropy density /s for any fluid always exceeds /(4k_B). A theoretical counterexample to this bound can be constructed from a nonrelativistic gas by increasing the number of species in the fluid while keeping the dynamics essentially independent of the species type. The question of whether the underlying structure of relativistic quantum field theory generically inhibits the realization of such a system and thereby preserves the possibility of a universal bound is considered here. Using rather conservative assumptions, it is shown here that a metastable gas of heavy mesons in a particular controlled regime of QCD provides a realization of the counterexample and is consistent with a well-defined underlying relativistic quantum field theory. Thus, quantum field theory appears to impose no lower bound on /s, at least for metastable fluids.

©2007 The American Physical Society

See Also

Comment on “Is There a `Most Perfect Fluid' Consistent with Quantum Field Theory?”
D. T. Son
Phys. Rev. Lett. 100, 029101 (2008)

Cohen Replies:
Thomas D. Cohen
Phys. Rev. Lett. 100, 029102 (2008)