GRB 221009A Gamma Rays from the Radiative Decay of Heavy Neutrinos?

We consider a mechanism that causes a decrease in the attenuation of high energy gamma-ray flux from gamma ray burst GRB 221009A. The mechanism is based on the existence of a heavy m_{N}∼(0.1-1) MeV mostly sterile neutrino N which mixes with active neutrinos. N's are produced in the gamma-ray burst (GRB) in π and K decays via mixing with ν_{µ}. They undergo the radiative decay N→νγ on the way to Earth. The usual exponential attenuation of gamma rays is lifted to an attenuation inverse in the optical depth. Various restrictions on this scenario are discussed. We find that the high energy γ events at 18 TeV can be explained if (i) the GRB active neutrino fluence is close to the observed limit, (ii) the branching ratio of N→νγ is at least of the order 10%.

Neutrino Self-Interactions and XENON1T Electron Recoil Excess.

The XENON1T collaboration recently reported an excess in electron recoil events in the energy range between 1-7 keV. This excess could be understood to originate from the known solar neutrino flux if neutrinos couple to a light vector mediator with strength g_{νN} that kinetically mixes with the photon with strength χ and g_{νN}χ∼10^{-13}. Here, we show that such coupling values can naturally arise in a renormalizable model of long-range vector-mediated neutrino self-interactions. The model could be distinguished from other explanations of the XENON1T excess by the characteristic 1/T^{2} energy dependence of the neutrino-electron scattering cross section. Other signatures include invisible Higgs and Z decays and leptophilic charged Higgses at a few 100 GeV. ALPS II will probe part of the viable parameter space.