Viscous Properties of One-Dimensional Fermi Gases

We present recent work on the hydrodynamics of one-dimensional and quasi-one-dimensional Fermi gases. A particular focus is on the bulk viscosity, a transport coefficient which is essential to the application of hydrodynamics. This classical description breaks down at frequencies large compared with the rate of fermion backscattering. This regime, which has been the subject of recent theoretical interest, is described by two-fluid behavior. As in the case of superfluid helium-4, the two-fluid regime requires not one but three bulk viscosities, which we calculate in the limit of weak interactions.