Abstract
We present the first detailed phenomenological analysis of a radiative Majorana neutrino mass model constructed from opening up a ∆L = 2 mass-dimension-11 effective operator constructed out of standard model fields. While three such operators are generated, only one dominates neutrino mass generation, namely {O}_{47}=overline{L^C}Loverline{Q^C}Loverline{Q}{Q}^C HH, where L denotes lepton doublet, Q quark doublet and H Higgs doublet. The under- lying renormalisable theory contains the scalars {S}_1sim left(overline{3},1,1/3right) coupling as a diquark, {S}_3sim left(overline{3},3,1/3right) coupling as a leptoquark, and Φ3 ∼ (3, 3, 2/3), which has no Yukawa couplings but does couple to S1 and S3 in addition to the gauge fields. Neutrino masses and mixings are generated at two-loop order. A feature of this model that is different from many other radiative models is the lack of proportionality to any quark and charged- lepton masses of the neutrino mass matrix. One consequence is that the scale of new physics can be as high as 107 TeV, despite the operator having a high mass dimension. This raises the prospect that ∆L = 2 effective operators at even higher mass dimensions may, when opened up, produce phenomenologically-viable radiative neutrino mass models. The parameter space of the model is explored through benchmark slices that are subject to experimental constraints from charged lepton flavour-violating decays, rare meson de- cays and neutral-meson mixing. The acceptable parameter space can accommodate the anomalies in RK (∗) and the anomalous magnetic moment of the muon.
Highlights
The minimal Standard Model (SM) features massless neutrinos
We present the first detailed phenomenological analysis of a radiative Majorana neutrino mass model constructed from opening up a ∆L = 2 mass-dimension-11 effective operator constructed out of standard model fields
Comparing the orders of magnitude of neutrino masses generated through the completions of the three operators, given in equations. (2.1), (2.2), and (2.3), we find that O25 and O55 are very suppressed compared to O47: mOν 25 ≤ Y b v2
Summary
The minimal Standard Model (SM) features massless neutrinos. the experimental observation of neutrino oscillations has established that at least two of the three known neutrinos are massive [1,2,3,4,5,6,7,8,9,10,11,12]. Classifying Majorana neutrino mass models using ∆L = 2 effective operators, each of which can be “opened up” (UV-completed at tree level) to produce neutrino self-energy diagrams, is a systematic way to approach the neutrino mass problem. It was believed that any exotic particles used to complete these models would have to be detectable at an energy scale that has already been probed [29] and dimension-11 operators that produce neutrino masses in agreement with current data at two-loop level or more would lie in a sweet spot — bringing the scale of BSM physics to a few TeV, an energy scale that is being directly probed at the Large Hadron Collider (LHC) and indirectly at precision- or luminosity-frontier experiments, and would be fully accessible at a future 100 TeV collider.
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