Neutrino decay catalyzed by the Mikheyev-Smirnov-Wolfenstein effect.

Abstract

A new mechanism for neutrino (\ensuremath{\nu}) decay in the Mikheyev-Smirnov-Wolfenstein (MSW) regime of weak mixing and small \ensuremath{\nu} mass differences is pointed out. Even though electron-neutrinos (${\ensuremath{\nu}}_{e}$) in this regime are practically stable, in solar matter, conversion of the ${\ensuremath{\nu}}_{e}$ to a ``heavier'' flavor by the MSW effect can catalyze \ensuremath{\nu} decay. MSW+\ensuremath{\nu} decay into Majorons can lead to a strong solar antineutrino signal in proposed experiments, directly probing \ensuremath{\nu}-Majoron couplings \ensuremath{\sim}700 times smaller than the present laboratory bound of ${g}^{2}$4.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$.