Particle decays in the presence of a neutrino background
  Several non-threshold reactions which may be used to detect the cosmic neutrino background are presented. The corresponding cross sections are calculated analytically within the Standard Model. These reactions are sensitive not only to the electron neutrinos but also to the muon and tau neutrinos. Some possibilities of experimental observation of the neutrino background are indicated. 
I. Alikhanov
astro-ph.CO hep-ph