Radiative neutrino decays and scattering experiments

Existing measurements of the total ν${¯}_e$ $e^{\mathrm{-}}$ cross section yield a very restrictive limit on the radiative decay of electron neutrinos, ${\mathrm{\tau }}_{\nu \mathit{e}}$ ${\mathit{m}}_{\nu }$ ${\mathit{e}}^3$≳3×${10}^{18}$ /sec ${\mathrm{eV}}^3$, which is even competitive with recent bounds from the nonobservation of γ rays from SN 1987A. Our bound is not valid if the neutrino electric and magnetic transition moments are exactly equal, a cancellation which can occur only if neutrinos are of Dirac type. This is a new example for the important differences in the electromagnetic properties of Dirac versus Majorana neutrinos.