Neutrino secret self-interactions: a booster shot for the cosmic
  neutrino background
  Neutrinos might interact among themselves through forces that have so far
remained hidden. Throughout the history of the Universe, such secret
interactions could lead to scatterings between the neutrinos from supernova
explosions and the non-relativistic relic neutrinos left over from the Big
Bang. Such scatterings can boost the cosmic neutrino background (C$\nu$B) to
energies of ${\cal O}$(MeV), making it, in principle, observable in experiments
searching for the diffuse supernova neutrino background. Assuming a
model-independent four-Fermi interaction, we determine the upscattered cosmic
neutrino flux, and derive constraints on such secret interactions from the
latest results from Super-Kamiokande. Furthermore, we also study prospects for
detection of the boosted flux in future lead-based coherent elastic
neutrino-nucleus scattering experiments.
