How to detect the cosmic neutrino background?

Abstract

A measurement of the big bang relic neutrinos would open a new window to the early universe. We review various possibilities to detect this cosmic neutrino background and substantiate the assertion that -- apart from the rather indirect evidence to be gained from cosmology and large-scale structure formation -- the annihilation of ultrahigh energy cosmic neutrinos with relic anti-neutrinos (or vice versa) on the Z-resonance is a unique process having sensititivy to the relic neutrinos, if a sufficient flux at E^res_{nu_i} = M_Z^2/(2 m_{nu_i}) = 4 x 10^{22} eV (0.1 eV/m_{nu_i}) exists. The associated absorption dips in the ultrahigh energy cosmic neutrino spectrum may be searched for at forthcoming neutrino and air shower detectors. The associated protons and photons may have been seen already in form of the cosmic ray events above the Greisen-Zatsepin-Kuzmin cutoff.