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 νν→ϕ and ν[over ¯]ν[over ¯]→ϕ 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_{ϕ} for 100  eV≲m_{ϕ}≲100  MeV. It is straightforward to extend our new argument to other hypothetical feebly interacting particles.