New Weinberg operator for neutrino mass and its seesaw origin

Abstract

We consider a new Weinberg operator for neutrino mass of the form $H_u\widetilde{H_d}{L}_i{L}_j$ involving two different Higgs doublets $H_u,H_d$ with opposite hypercharge, where $\widetilde{H_d}$ is the charge conjugated doublet. It may arise from a model where the two Higgs doublets carry the same charge under a $U(1{)}^{\prime }$ gauge group which forbids the usual Weinberg operator but allows the mixed one. The new Weinberg operator may be generated via two right-handed neutrinos oppositely charged under the $U(1{)}^{\prime }$, which may be identified as components of a fourth vector-like family in a complete model. Such a version of the type I seesaw model, which we refer to as type Ib to distinguish it from the usual type Ia seesaw mechanism which yields the usual Weinberg operator, allows the possibility of having potentially large violations of unitarity of the leptonic mixing matrix whose bounds we explore. We also consider the relaxation of the unitarity bounds due to the further addition of a single right-handed neutrino, neutral under $U(1{)}^{\prime }$, yielding a usual type Ia seesaw contribution.

19 pages, 6 figures. v2: minor typos corrected and references added

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Cited by in corpus (8)

• The symmetry approach to quark and lepton masses and mixing
• Fermion mass hierarchies from vector-like families with an extended 2HDM and a possible explanation for the electron and muon anomalous magnetic moments
• Dark Matter in the Type Ib Seesaw Model
• Neutrino masses from new Weinberg-like operators: Phenomenology of TeV scalar multiplets
• Neutrino masses from new seesaw models: Low-scale variants and phenomenological implications
• Connecting $(g-2{)}_{\mu }$ to neutrino mass in the extended neutrinophilic 2HDM
• $Z$ mediated Flavour Changing Neutral Currents with a Fourth Vector-Like Family
• Spontaneously stabilised dark matter from a fermiophobic $U(1{)}^{\prime }$ gauge symmetry