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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---νₑ, ν_μ, {ν}ₑ, or {ν}_μ---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^-9[m_ν/(1 keV )] sec {}{τ}{}5×{}10⁷[m_ν/(1 keV] sec. This places severe constraints on models for Simpson's 17-keV neutrino.
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Dodelson et al. (1992) studied this question.
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