We present a SU(2${)}_{\mathit{H}}$ model that can simultaneously accommodate a 17-keV pseudo Dirac neutrino ${\nu }_{\mathrm{\tau }}$ as well as a large transition magnetic moment for nearly massless ${\nu }_{\mathit{e}}$ and ${\nu }_{\mathrm{\mu }}$. While the small Dirac term is generated radiatively, the mass corrections for the light neutrinos remain suppressed even on breaking the Voloshin-type SU(2${)}_{\nu }$ symmetry. The cosmological constraints are met by a rapid decay of the ${\nu }_{\mathrm{\tau }}$ into a ${\nu }_{\mathrm{\mu }}$ and a singlet-doublet Majoron.

• Received 27 February 1992

DOI:https://doi.org/10.1103/PhysRevLett.68.2875