CP violation in the lepton sector with small neutrino masses

Abstract

Small, even vanishing neutrino masses are consistent with large CP violation effects in the leptonic sector. As an example, and a proof of existence of this situation, we present a model based on the SU(2)L x SU(2)R x U(1) gauge symmetry, where the fermion content has been Extended to include a gauge singlet lepton SL. Interesting features of this model (which should be seen as a mere example) are: (1) neutrino masses can either vanish or be in the range where the Mikheyev-Smirnov-Wolfenstein (MSW) mechanism for the solar neutrino puzzle is operative, and (2) CP violation effects in the lepton sector are manifestly large and therefore accessible to current experiments. In particular, it is found that the electron electric dipole moment, drme, can be of order 10-24e[middle dot]cm; if generation mixing is negligible, the [mu] longitudinal polarization, PrmL, in the decay can be in the range 10-10-10-3.