Radiative fermion masses and large neutrino magnetic moment: A unified picture

A large transition magnetic moment of the neutrino (needed to explain the apparent anticorrelation of the solar-neutrino flux with the sunspots) can be reconciled with a naturally small neutrino mass by gauging the horizontal SU(2) symmetry connecting the electron and the muon generations. In this paper, we show that the same symmetry, when extended to the quark sector, provides a radiative picture for fermion masses, thereby explaining qualitatively the observed mass and mixing hierarchy among charged fermions. The neutrino masses arise in the model only at the two-loop level, whereas the magnetic moment is a one-loop effect. The neutrino is predicted to be a pseudo Dirac particle with mν∼1--10 eV and δmν2∼10-7 eV2