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In the minimal standard electroweak gauge model, there is an effective dimensionfive 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 righthanded neutrino. Another is having a heavy Higgs triplet as recently proposed. The third possibility is to have(More)
With the accumulation of many years of solar and atmospheric neutrino oscillation data, the approximate form of the 3 × 3 neutrino mixing matrix is now known. The theoretical challenge is to understand where this mixing matrix comes from. Recently, a remarkable fact was discovered that for a specific pattern of the neutrino mass matrix at a high scale, any(More)
If the recently discovered anomalous events at HERA are due to a scalar leptoquark, then it is very likely to have weak isospin I = 1/2. In that case, present precision measurements of the oblique radiative parameters S and T provide strong constraints on the mass of the other component of this doublet. If the standard model is extended to include such a(More)
A heavy triplet of leptons (Σ,Σ,Σ)R per family is proposed as the possible anchor of a small seesaw neutrino mass. A new U(1) gauge symmetry is then also possible, and the associated gauge boson X may be discovered at or below the TeV scale. We discuss the phenomenology of this proposal, with and without possible constraints from the NuTeV and atomic parity(More)
If the standard model of quark interactions is supplemented by a discrete A4 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 A4 is proposed, which results in a realistic(More)
The successful A4 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 |Vub| and the CP phase β, thus allowing for a decisive future test of this model. Since the original(More)