Radiative neutrino decays and scattering experiments

Existing measurements of the total {ν}ₑ{e}^{{{-}}}$ cross section yield a very restrictive limit on the radiative decay of electron neutrinos, ${{{τ}}}_{{ν}e}m_ν{e}³3×{10}¹⁸$ /sec ${eV}³$, 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.