Consequences of Massive Neutrino to Astrophysics and Cosmology

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It is now recognized that a neutrino is a massive spin-1/2 particle. Consequently, neutrino- antineutrino pair production and their pair annihilation are theoretically valid processes. The data prove that the strength of weak interactions increases with collision energy. Therefore, a neutrino pair production event is expected to be a significant process in the region which is just outside the event horizon of a black hole. Another neutrino source is the pair production of particles like muons and charged pions whose decay produces neutrinos. Similarly, copious neutrino pair production events are expected to take place right after the big bang. Since a neutrino does not directly participate in electromagnetic interactions, its pair annihilation cannot directly produce photons. For this reason, a low energy neutrino-antineutrino collision can only go to another neutrino-antineutrino pair. It follows that the number of low energy neutrinos increases with time. This effect may contribute to the problem of the missing mass of the universe.