The cosmic neutrino clustering and the isotropy of background radiation

Different from the ordinary matter, there is no electromagnetic interaction between the neutrino and the radiation. Consequently, the cosmic massive neutrino gas could cluster under self-gravitation even before the epoch of the recombination. However, there is gravitational coupling between the neutrino and the ordinary matter. Through this coupling the ordinary matter could follow the clustering of the neutrino at least partially. (Auth.)