Upper limits on the cosmic neutrino background from cosmic rays
Extragalactic and galactic cosmic rays scatter with the cosmic neutrino background during propagation to Earth, yielding a flux of relic neutrinos boosted to larger energies. If an overdensity of relic neutrinos is present in galaxies, and neutrinos are massive enough, this flux might be detectable by high-energy neutrino experiments. For a lightest neutrino of mass 𝑚 𝜈 ∼0.1 eV, we find an upper limit on the local relic neutrino overdensity of ∼10 13 and an upper limit on the relic neutrino overdensity at TXS 0506 + 056 of ∼10 10 . Future experiments like GRAND or IceCube-Gen2 could improve these bounds by orders of magnitude.