Generating Majorana neutrino masses with loops

We give a review on neutrino models in which Majorana neutrino masses are generated radiatively through loop diagrams. In particular, we concentrate on the two-loop models which contain extra doubly charged singlet Phi and triplet Delta scalars beyond the Standard Model so that the new Yukawa. Psi(l) over bar (c)(R)l(R) and effective Psi W-+/-+/--/+ W -/+ couplings can be induced. In these two-loop models, we find that the neutrino mass spectrum is a normal hierarchy and the rate of the neutrinoless double beta decay (0 nu beta beta) can be large as it is dominated by the short-distance tree contribution. In addition, by using the neutrino oscillation data and comparing with the global fitting result in the literature, we find a unique neutrino mass matrix and predict the Dirac and two Majorana CP phases to be 3(pi - eta)/2, pi + 3 eta/2 and (3 pi - eta)/2 with eta = 0.07 pi, respectively.