Discovery of such features would thus provide invaluable information on more fundamental theories. Neutrino properties are of interest not only in particle physics theories, but also in astrophysics and cosmology. Indeed neutrinos play an important role in stellar physics. The solar neutrino anomaly, namely the observation on earth of a solar neutrino flux less than that expected, may be explained by neutrino masses or a neutrino magnetic moment. Relic neutrinos from the big bang, if they have mass, may be part of the invisible mass of the universe.
Astrophysical observations indicate that most of the matter in the universe is invisible.
Neutrinos interact very weakly, especially at low energy. For that reason the event rate in neutrino experiments is very low. Special care has to be taken to reduce the background, which might mimic interesting events. Whenever possible the experiments are performed underground, to substantially reduce the background from cosmic rays. Materials of low intrinsic radioactivity have to be selected for the construction of the detectors.