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Edward Taylor and Mohit Randeria
The Ohio State University
The viscosity of strongly interacting systems is a topic of great interest in diverse fields.
We focus here on the bulk and shear viscosities of emph{non-relativistic} quantum fluids, with particular emphasis on
strongly interacting ultracold Fermi gases. We use Kubo formulas for the bulk and shear viscosity spectral functions,
$zeta(omega)$ and $eta(omega)$ respectively, to derive exact, non-perturbative results.
Our results include: a microscopic connection between the shear viscosity $eta$ and the normal fluid density $
ho_n$;
sum rules for $zeta(omega)$ and $eta(omega)$ and their evolution through the BCS-BEC crossover;
universal high-frequency tails for $eta(omega)$ and the dynamic structure factor $S({f q}, omega)$.
We use our sum rules to show that, at unitarity, $zeta(omega)$ is identically zero and thus relate
$eta(omega)$ to density-density correlations.
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