Strong Supernova 1987A Constraints on Bosons Decaying to Neutrinos

Majoron-like bosons would emerge from a supernova (SN) core by neutrino coalescence of the form & nu;& nu; -& phi; and & nu; over bar & nu; over bar -& phi; with 100-MeV-range energies. Subsequent decays to (anti)neutrinos of all flavors provide a flux component with energies much larger than the usual flux from the "neutrino sphere." The absence of 100-MeV-range events in the Kamiokande-II and Irvine-Michigan-Brookhaven signal of SN 1987A implies that less than 1% of the total energy was thus emitted and provides the strongest constraint on the Majoron-neutrino coupling of g < 10-9 MeV/m & phi; for 100 eV < m & phi; < 100 MeV. It is straightforward to extend our new argument to other hypothetical feebly interacting particles.