Constraints to the decays of Dirac neutrinos from SN 1987A

The wrong-helicity states of keV-mass Dirac neutrinos are emitted copiously from the cores of newly born neutron stars, including that associated with SN 1987A. If they decay into proper-helicity neutrinos—${\nu }_{\mathit{e}}$, ${\nu }_{\mathrm{\mu }}$, ν${\mathrm{¯}}_{\mathit{e}}$, or ν${\mathrm{¯}}_{\mathrm{\mu }}$—they should have produced distinctive high-energy events in the Kamiokande II and Irvine-Michigan-Brookhaven detectors. The absence of such events excludes these decay modes for a Dirac neutrino of mass between order 1 and 300 keV and lifetime ${10}^{\mathrm{-}9}$[${\mathit{m}}_{\nu }$/(1 keV )] sec ≲τ≲5×${10}^7$[${\mathit{m}}_{\nu }$/(1 keV] sec. This places severe constraints on models for Simpson’s 17-keV neutrino.