17 keV NEUTRINO AND MAJORON MODELS

A model for the 17 keV Dirac neutrino is considered in the framework of the SU(2)×U(1) theory. No right-handed neutrinos are introduced. The Dirac mass for the neutrino arises from the L_e+L_τ–L_μ invariant couplings of the left-handed neutrinos to an SU(2) triplet. An SU(2) singlet field is introduced to suppress the Majoron coupling to the Z. This makes the model consistent with the LEP results on the invisible Z width. The singlet vacuum expectation value ω is constrained to be ≤O(80 MeV) from cosmological considerations. For, ω≈80 MeV, the 17 keV neutrino is shown to provide the bulk of the dark matter.