Exact one-loop results for l_i rightarrow l_jgamma in 3-3-1 models

L T Hue,L D Ninh,T T Thuc,N T T Dat

doi:10.1140/epjc/s10052-018-5589-3

Abstract

We investigate the decays l_irightarrow l_j gamma , with l_i=e,mu ,tau in a general class of 3-3-1 models with heavy exotic leptons with arbitrary electric charges. We present full and exact analytical results keeping external lepton masses. As a by product, we perform numerical comparisons between exact results and approximate ones where the external lepton masses are neglected. As expected, we found that branching fractions can reach the current experimental limits if mixings and mass differences of the exotic leptons are large enough. We also found unexpectedly that, depending on the parameter values, there can be huge destructive interference between the gauge and Higgs contributions when the gauge bosons connecting the Standard Model leptons to the exotic leptons are light enough. This mechanism should be taken into account when using experimental constraints on the branching fractions to exclude the parameter space of the model.

Highlights

Br(μ− → e−γ ) < 4.2 × 10−13, Br(τ − → e−γ ) < 3.3 × 10−8, Br(τ − → μ−γ ) < 4.4 × 10−8. (1)From theoretical side, the processes li → l j γ are loop induced
We investigate the decays li → l j γ, with li = e, μ, τ in a general class of 3-3-1 models with heavy exotic leptons with arbitrary electric charges
We have provided full and exact analytical results for the li → l j γ partial decay widths for a general class of 3-3-1 models with exotic leptons and with arbitrary β

Summary

Introduction

In the general class of 3-3-1 models here considered, there is one important parameter usually called β, which together with X , the new charge corresponding to the group U (1)X , define the electric-charge operator. Since we consider a general class of models with arbitrary β, this mixing effect will be neglected This is justified because we will assume that the new leptons are much heavier than the SM leptons. For the Higgs sector, we assume A, B = 0, ±1, so that only the following mixings of scalar fields with the same electric charge are allowed: (χA, ηA), (χB , ρB ), (ρ+, η+) and (χ 0, ρ0, η0). Bosonic particles with electric charges of ±B are not involved in the present calculation Their masses and mixing angles are provided above for the sake of completeness.

Analytical results

E R tv2 u h

Numerical results

Exotic-lepton contribution

Conclusions