Neutrino Self-Interaction

Neutrino is a massless, feebly-interacting particle in SM. However, it is known that neutrino should be massive. New physics is guaranteed to exist in the neutrino sector. Basic question naturally raises regarding neutrino physics. What is the source of neutrino mass? Can neutrino have self-interactions?

With one neutrino flavor still being relativistic today, the resonance of the scattering between incoming DSNB neutrino and cosmic neutrino background can be significantly widened. The distortion of the DSNB spectrum can thus be used to probe a much wider parameter space of neutrino self-interaction. We show that a mediator at eV scale can be probed with the coupling to neutrino as low as $10^{-8}$.