  Collective interactions of a beam of neutrinos/antineutrinos traversing a
dense magnetized plasma of electrons/positrons, protons and neutrons are
studied with particular reference to the case of a Supernova. We find that the
ponderomotive force exerted by neutrinos gives, contrary to expectations, a
negligible contribution to the revival of the shock for a successful Supernova
explosion, although new types of convection and plasma cooling processes
induced by the ponderomotive force could be, in principle, relevant for the
dynamics itself.
