  Fermi gases with short-range interactions are ubiquitous in ultracold atomic
systems. In the absence of spin-flipping processes the number of atoms in each
spin species is conserved separately, and we discuss the associated Ward
identities. For contact interactions the spin conductivity spectral function
sigma_s(omega) has universal power-law tails at high frequency. We derive the
spin f-sum rule and show that it is not affected by these tails in d<4
dimensions. Likewise the shear viscosity spectral function eta(omega) has
universal tails; in contrast they modify the viscosity sum rule in a
characteristic way.
