Abstract
We investigate the radiative generation of lepton masses and mixing angles in the Standard Model extended by one right-handed neutrino and one extra Higgs doublet. We assume approximate rank-1 Yukawa couplings at a high energy scale and we calculate the one loop corrected charged lepton and neutrino mass matrices at the low energy scale. We find that quantum effects generate, for typical high energy parameters, a hierarchy between the muon and the tau mass, a hierarchy between the solar and the atmospheric mass splittings, and a pattern of leptonic mixing angles in qualitative agreement with experiments.
Highlights
JHEP11(2014)089 of the see-saw mechanism is automatically cured by introducing a second Higgs doublet
We investigate the radiative generation of lepton masses and mixing angles in the Standard Model extended by one right-handed neutrino and one extra Higgs doublet
As discussed in [17, 18], even if the tree level neutrino masses display very large hierarchies, quantum effects induced by the second Higgs doublet generate a mild hierarchy between the heaviest and next-to-heaviest neutrino masses which is, for well motivated choices of the high energy parameters, in qualitative agreement with the value inferred from oscillation experiments
Summary
We consider the impact of quantum effects on the scenario presented in the previous section, where the Standard Model is extended with one extra Higgs doublet and one righthanded neutrino, under the assumption that all Yukawa couplings are rank-1 at a cut-off scale Λ ≫ Mmaj. As discussed in [17, 18], quantum effects in the two Higgs doublet model increase the rank of this coupling, breaking the degeneracy among the eigenvalues and fixing univocally the angles of the mixing matrix. It is straightforward to calculate the leading contributions to the charged lepton and neutrino masses, as well as to the leptonic mixing matrix, in terms of the parameters defining the Yukawa couplings at the cut-off scale, Yx(a)(Λ), x = e, ν, u, d. In the case α = 0 one recovers the zero-th order structure of the CKM matrix derived in [19] In this framework the different pattern of mixing angles in the quark and lepton sectors is related to the amount of misalignment of the tree level (rank-1) Yukawa couplings to the Higgs Φ1, parametrized by one single angle α. The measured leptonic mixing angles can be accommodated in this framework for generic high energy Yukawa structures, namely Yukawa matrices with mixing angles which are neither maximal nor small
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