Resonant spin-flavor precession of solar and supernova neutrinos

The combined effect of matter and magnetic fields on neutrino spin and flavor precession is examined. We find a potential new kind of resonant solar-neutrino conversion ν/sub e//sub >//sub L//sub =/→ν/sub μ//sub =/ or ν/sub tau//sub >//sub R//sub =/ (for Dirac neutrinos) or ν/sub e/→nu-bar/sub μ/ or nu-bar/sub tau/ (for Majorana neutrinos). Such a resonance could help account for the lower than expected solar-neutrino ν/sub e/ flux and/or indications of an anticorrelation between fluctuations in the ν/sub e/ flux and sunspot activity. Consequences of spin-flavor precession for supernova neutrinos are also briefly discussed