Abstract
We study charged lepton flavor violation for the three most popular 3-loop Majorana neutrino mass models. We call these models “minimal” since their particle content correspond to the minimal sets for which genuine 3-loop models can be constructed. In all the three minimal models the neutrino mass matrix is proportional to some powers of Standard Model lepton masses, providing additional suppression factors on top of the expected loop suppression. To correctly explain neutrino masses, therefore large Yukawa couplings are needed in these models. We calculate charged lepton flavor violating observables and find that the three minimal models survive the current constraints only in very narrow regions of their parameter spaces.
Highlights
These three models are probably the best-known 3-loop models in the literature, and a number of other papers have studied them
We describe the scalar fields in these three minimal scenarios, the way the electroweak symmetry gets broken in each case and the Yukawa interactions with the SM fermions
The cocktail model is an example of a type-II-seesaw-like model
Summary
In order to make the discussion more transparent for the reader, it is convenient to adopt a common notation and use the same conventions for the three models considered here. The 2HDM scalar sector is composed of two scalar doublets, Φ1 and Φ2, with identical quantum numbers under the SM gauge symmetry, as shown in table 3 They can be decomposed in terms of their SU(2)L components as. Since both scalar doublets have exactly the same quantum numbers, and in particular since they will both be assumed to be even under the Z2 symmetry, flavor changing neutral current interactions are in principle present. This dangerous feature can be fixed by introducing a second (softly broken) Z2 symmetry, under which one of the two doublets and some of the SM fermions are charged.
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