Study of lepton flavor violation in flavor symmetric models for lepton sector

Abstract

Flavor symmetric model is one of the attractive Beyond Standard Models (BSMs) to reveal the flavor structure of the Standard Model (SM). A lot of efforts have been put into the model building and we find many kinds of flavor symmetries and setups are able to explain the observed fermion mass matrices. In this paper, we look for common predictions of physical observables among the ones in flavor symmetric models, and try to understand how to test flavor symmetry in experiments. Especially, we focus on the BSMs for leptons with extra Higgs SU(2) L doublets charged under flavor symmetry. In many flavor models for leptons, remnant symmetry is partially respected after the flavor symmetry breaking, and it controls well the Flavor Changing Neutral Currents (FCNCs) and suggests some crucial predictions against the flavor changing process, although the remnant symmetry is not respected in the full lagrangian. In fact, we see that τ − → e + µ − µ − (µ + e − e − ) and e + e − → τ + τ − (µ − µ + ) processes are the most important in the flavor models that the extra Higgs doublets belong to triplet representation of flavor symmetry. For instance, the stringent constraint from the µ → eγ process could be evaded according to the partial remnant symmetry. We also investigate the breaking effect of the remnant symmetry mediated by the Higgs scalars, and investigate the constraints from the flavor physics: the flavor violating τ and µ decays, the electric dipole moments, and the muon anomalous magnetic moment. We also discuss the correlation between FCNCs and nonzero θ 13 , and point out the physical observables in the charged lepton sector to test the BSMs for the neutrino mixing.

Flavon-induced connections between lepton flavour mixing and charged lepton flavour violation processes

“…In A 4 models, the only processes allowed by the Z 3 residual symmetry are τ − → µ + e − e − , τ − → e + µ − µ − , and all other 3-body and radiative decays are forbidden [67,68]. The latter can take place if the Z 3 symmetry is broken [69], but are typically suppressed due to the consistency with oscillation data, as shown later. Current experimental bounds of the branching ratios of LFV τ 3-body decays τ − → µ + e − e − , e + µ − µ − , µ + µ − µ − , e + e − µ − , µ + µ − e − , e + e − e − , and ratiative decays τ − → µ − γ, e − γ are in general around 10 −8 , measured by Belle [70] and BaBar [71], respectively.…”

“…(3.9) in the limit m 2 → ∞ and ϑ → −45 • . Only in the limit ϑ → 0, τ − → µ + e − e − is suppressed, as discussed in [69].…”

Higgs Lepton Flavor Violating Decays in Two Higgs Doublet Models

“…These can be used to set a lower limit on the HLFV rates [83]. For instance, one finds BR(h → τ µ) 10 −6 10 −7 (39) for normal (inverted) neutrino mass ordering. We refer to [83], where a detailed exploration of the parameter space of the Zee model is performed, concluding that the model can accommodate large HLFV rates, even exceeding the current bounds.…”

Minimal models of loop-induced lepton flavor violation in Higgs boson decays

“…In muon-electron conversion, the amplitude is obtained from the exchange of either a Higgs or gauge boson (γ or Z, depicted in Fig. 8) between a loop of virtual vectorlike fermions that are connected nucleons through 9 Recall that the set of couplings λi in τ − µ sector is independent from its counterpart in the µ − e. 10 Either Qαem or g…”