  I summarize the results of a recent analysis where the cosmological effects
of interactions of neutrinos with cold Dark Matter (DM) is investigated. This
interaction produces diffusion-damped oscillations in the matter power
spectrum, analogous to the acoustic oscillations in the baryon-photon fluid. I
discuss the bounds from the Sloan Digital Sky Survey on the corresponding
opacity defined as the ratio of neutrino-DM scattering cross section over DM
mass, and compare with the constraint from observation of neutrinos from
supernova 1987A.
