Macroscopic Forces driven by Resonant Neutrino Conversion

We show that neutrino oscillations in matter are always accompanied by collective forces on the medium. This effect may produce interesting consequences for the background and the neutrino oscillations themselves. The force is maximal in the case of resonant neutrino conversion in the adiabatic regime. We study here the forces driven by $\nu_e-\nu_{\mu,\tau}$ and $\nu_e-\nu_s$ MSW conversion and shortly discuss their possible relevance for the dynamics of a type II supernova.