Inertial effects in the response of viscous and viscoelastic fluids.

We consider the effect of inertia on the high frequency response of a general linear viscoelastic material to local deformations. We calculate the displacement response and correlation functions for points separated by a distance r. The effects of inertia and incompressibility lead to anticorrelations in the correlation or response functions, which become more pronounced for more elastic materials. Furthermore, the stress propagation in viscoelastic media is no longer diffusive, as for simple liquids.