Neutrino Magnetic Moments, Flavor Mixing, and the Super-Kamiokande Solar Data

Abstract

We find that magnetic neutrino-electron scattering is unaffected by oscillations for vacuum mixing of Dirac neutrinos with only diagonal moments and for Majorana neutrinos with two flavors. For Mikheyev-Smirnov-Wolfenstein mixing, these cases are again obtained, though the effective moments can depend on the neutrino energy. Thus, e.g., the magnetic moments measured with ${\overline{\ensuremath{\nu}}}_{e}$ from a reactor and ${\ensuremath{\nu}}_{e}$ from the Sun could be different. With minimal assumptions, we find a new limit on ${\ensuremath{\mu}}_{\ensuremath{\nu}}$ using the 825-d Super-Kamiokande solar neutrino data: $|{\ensuremath{\mu}}_{\ensuremath{\nu}}|\ensuremath{\le}1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}{\ensuremath{\mu}}_{B}$ at $90%$ CL, comparable to the existing reactor limit.