A minimal extension of the Standard Model is proposed, where the observed lefthanded 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 experiments at the Large Hadron Collider.
In the minimal standard electroweak gauge model, there is an effective
dimension-five operator which generates neutrino masses, and it has only three
tree-level realizations. One is the canonical seesaw mechanism with a
right-handed neutrino. Another is having a heavy Higgs triplet as recently
proposed. The third is to have a heavy Majorana fermion triplet, an example of
which is presented here in the context of supersymmetric SU(5) grand
unification. The three generic one-loop realizations of this operator are also
discussed.Comment: 12 pages including 5 figures; corrected minus signs in Eqs.(5)-(6),
no result is affecte
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. \underline {Naturally}
small Majorana neutrino masses would become possible, as well as leptogenesis
in the early universe which gets converted at the electroweak phase transition
into the present observed baryon asymmetry.Comment: 12 pages including one figur
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 supersymmetry. The quark mixing matrix is also calculable in a similar way. The mixing parameter U e3 is predicted to be imaginary, leading to maximal CP violation in neutrino oscillations. Neutrinoless double beta decay and τ → µγ should be in the experimentally accessible range.
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