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 $\nu \nu \to \phi$ and $\bar{\nu }\bar{\nu }\to \phi$ 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 $g\lesssim {10}^{-9}\mathrm{M}\mathrm{e}\mathrm{V}\mathrm{/}{m}_{\phi }$ for $100\mathrm{e}\mathrm{V}\lesssim m_{\phi }\lesssim 100\mathrm{M}\mathrm{e}\mathrm{V}$. It is straightforward to extend our new argument to other hypothetical feebly interacting particles.