Strong Supernova 1987A Constraints on Bosons Decaying to Neutrinos

Multimessenger Constraints on Radiatively Decaying Axions from GW170817

The metastable hypermassive neutron star produced in the coalescence of two neutron stars can copiously produce axions that radiatively decay into O(100)  MeV photons. These photons can form a fireball with characteristic temperature smaller than 1 MeV. By relying on x-ray observations of GW170817/GRB 170817A with CALET CGBM, Konus-Wind, and Insight-HXMT/HE, we present new bounds on the axion-photon coupling for axion masses in the range 1-400 MeV. We exclude couplings down to 5×10^{-11}  GeV^{-1}, complementing and surpassing existing constraints. Our approach can be extended to any feebly interacting particle decaying into photons.

Large Neutrino Secret Interactions Have a Small Impact on Supernovae

When hypothetical neutrino secret interactions (νSI) are large, they form a fluid in a supernova (SN) core, flow out with sonic speed, and stream away as a fireball. For the first time, we tackle the complete dynamical problem and solve all steps, systematically using relativistic hydrodynamics. The impact on SN physics and the neutrino signal is remarkably small. For complete thermalization within the fireball, the observable spectrum changes in a way that is independent of the coupling strength. One potentially large effect beyond our study is quick deleptonization if νSI violate lepton number. By present evidence, however, SN physics leaves open a large region in parameter space, where laboratory searches and future high-energy neutrino telescopes will probe νSI.