A minimal extension of the Standard Model is proposed, where the observed left-handed neutrinos obtain naturally small Majorana masses from a one-loop radiative seesaw mechanism. This model has two candidates (one bosonic and one fermionic) for the dark matter of the Universe. It has a very simple structure and should be verifiable in forthcoming… (More)
A simple and economical extension of the minimal standard electroweak gauge model (without right-handed neutrinos) by the addition of two heavy Higgs scalar triplets would have two significant advantages. Naturally small Majorana neutrino masses would become possible, as well as leptogenesis in the early universe which gets converted at the electroweak… (More)
The discrete non-Abelian symmetry A 4 , valid at some high-energy scale, naturally leads to degenerate neutrino masses, without spoiling the hierarchy of charged-lepton masses. Realistic neutrino mass splittings and mixing angles (one of which is necessarily maximal and the other large) are then induced radiatively in the context of softly broken… (More)
If the generating mechanism for neutrino mass is to account for both the newly observed muon anomalous magnetic moment as well as the present experimental bounds on lepton flavor nonconservation, then the neutrino mass matrix should be almost degenerate and the underlying physics should be observable at future colliders. We illustrate this assertion with… (More)
The leptonic Higgs doublet model of neutrino masses is implemented with an A 4 discrete symmetry (the even permutation of 4 objects or equivalently the symmetry of the tetrahedron) which has 4 irreducible representations: 1, 1 ′ , 1 ′′ , and 3. The resulting spontaneous and soft breaking of A 4 provides a realistic model of charged-lepton masses as well as… (More)
I review some of the recent progress (up to September 2005) in applying non-Abelian discrete symmetries to the family structure of leptons, with particular emphasis on the tribimaximal mixing ansatz of Harrison, Perkins, and Scott.
The successful A 4 family symmetry for leptons is applied to quarks, motivated by the quark-lepton assignments of SU(5). Realistic quark masses and mixing angles are obtained, in good agreement with data. In particular, we find a strong correlation between |V ub | and the CP phase β, thus allowing for a decisive future test of this model.
If the standard model of quark interactions is supplemented by a discrete A 4 symmetry (which may be relevant for the lepton sector), the spontaneous breaking of the electroweak gauge symmetry allows arbitrary quark masses, but all mixing angles are predicted to be zero. A pattern of the explicit breaking of A 4 is proposed, which results in a realistic… (More)
In the minimal standard electroweak gauge model, there is an effective dimension-five operator which generates neutrino masses. I show that there are three tree-level realizations of this operator. One is the canonical seesaw mechanism with a right-handed neutrino. Another is having a heavy Higgs triplet as recently proposed. The third possibility is to… (More)
In the recent successful applications of the non-Abelian discrete symmetry A 4 to the tribimaximal mixing of neutrinos, lepton doublets and singlets do not transform in the same way. It appears thus to be unsuitable as a family symmetry in grand unification. A simple resolution of this dilemma is proposed.