Supernova 1987A and the secret interactions of neutrinos

By using SN1987A as a ``source'' of neutrinos with energy app10 MeV we place limits on the couplings of neutrinos with cosmic background particles. Specifically, we find that the Majoron--electron-neutrino coupling must be less than about 10^-3; if neutrinos couple to a massless vector particle, its dimensionless coupling must be less than about 10^-3; and if neutrinos couple with strength g to a massive boson of mass M, then g/M must be less than 12 MeV^-1.