Resonant neutrino oscillations and stellar collapse

The Mikheyev-Smirnov-Wolfenstein mechanism for resonant amplification of neutrino oscillations is shown to occur in collapsing presupernova stellar cores if there exist massive unstable neutrinos which mix with the electron neutrino. The relevant massive neutrino mass range is 200 eV to 25 keV, and the required vacuum mixing angle is 10 to the -6th rad or greater. Neutrinos with these characteristics have been independently proposed to solve some galaxy formation problems and are suggested by familon models of the weak interaction. It is shown that adiabatic conversion of electron neutrinos into such massive neutrinos would occur during stellar collapse with resultant readjustment of lepton numbers and small entropy generation. These changes have implications for the supernova explosion mechanism.