Abstract
In this paper, a followup of arXiv: 1802.05722, we describe the many pathways to generate Dirac neutrino mass through dimension-6 operators. By using only the Standard Model Higgs doublet in the external legs one gets a unique operator $\frac{1}{\Lambda^2} \, \bar{L}\, \bar{\Phi} \, \bar{\Phi} \, \Phi \, \nu_R $. In contrast, the presence of new scalars implies new possible field contractions, which greatly increase the number of possibilities. Here we study in detail the simplest ones, involving $SU(2)_L$ singlets, doublets and triplets. The extra symmetries needed to ensure the Dirac nature of neutrinos can also be responsible for stabilizing dark matter.
Highlights
Elucidating the nature of neutrinos constitutes a key open challenge in particle physics
B 781, 122 (2018)], we describe the many pathways to generate Dirac neutrino mass through dimension-six operators
One appealing possibility is the quarticity symmetry, which was originally suggested in [11,12,13]. This mechanism uses a version of Uð1ÞL lepton number symmetry broken into its subgroup Z4
Summary
Elucidating the nature of neutrinos constitutes a key open challenge in particle physics. Dirac neutrinos are not generally expected within a gauge theoretic framework [8], they arise in models with extra dimensions [9,10], where the νR states are required for the consistent high energy completion of the theory. Here and quite generically, the extra symmetries needed to ensure the Dirac nature of neutrinos can be made responsible for stability of dark matter.
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