Models of neutrino masses and mixings: implications of neutrinoless double beta decay

One of the most important features of neutrinos is that they could be Majorana particles, which violates lepton number. This can be verified in neutrinoless double beta (0νββ) decay experiments. An evidence for neutrinoless double beta decay has recently been announced, which has several very strong implications, some of which will be reviewed briefly in this article. If the neutrinos are Majorana particles violating lepton number, then the Majorana masses could explain the baryon asymmetry of the universe. The solar, atmospheric and other laboratory experiments give us the mass squared difference between different neutrinos; only the (0νββ) decay can give us the absolute masses. The latest result from (0νββ) decay restricts the patterns of neutrino masses to very few choices, only the degenerate and the inverted hierarchical mass matrices are allowed for three generations of neutrinos. The allowed textures of the neutrino masses are also constrained. (author)