Constraint on the Mass and Lifetime of Heavy Neutrinos From the Supernova 1987a in the Large Magellanic Cloud

If heavy neutrinos were emitted from the supernova 1987A in the Large Magellanic Cloud (LMC) and decayed outside the star, a γ-ray burst would have been observed after the ν-burst. If this γ-ray burst was not observed, it would impose a constraint on the mass, m v , and lifetime, τ ν , of heavy neutrinos. We investigate this constraint on the assumption that the γ-ray burst was not observed and obtain a more stringent constraint than that imposed by cosmology. We find that the range of mass and lifetime of tau neutrinos (m v ~50 MeV , τ ν ~10 3 sec ), which is allowed by previous constraints from experiments and cosmology, is completely prohibited by the present constraint provided that the radius of the progenitor of this supernova is less than 10 13 cm .