Phenomenology of a lepton triplet

Abstract

The most general phenomenological model involving a lepton triplet with hypercharge $\pm 1$ is constructed. A distinctive feature of this model is the prediction of a doubly charged lepton, and a new heavy Dirac neutrino. We study the phenomenology of these exotic leptons in both low-energy experiments and at the LHC. The model predicts FCNC processes such as rare muon decays, which are studied in detail in order to constrain the model parameters. All the decay channels of the exotic leptons are described for a wide range of parameters. It is found that, if the mixing parameters between the exotic and light leptons are not too small ($>10^{-6}$), then they can be observable to a $3-5\sigma$ statistical significance at the 7 TeV LHC with 10-50 fb$^{-1}$ luminosity for a 400 GeV mass, and 14 TeV with 100-300 fb$^{-1}$ luminosity for a 800 GeV mass.Comment: 28 pages, 17 figures. Version to appear in PR

Triplet with a doubly-charged lepton at the LHC

“…In the following we will closely follow the notation used in [17]: the mass matrices in the singly-charged and neutral sectors can be diagonalised by two unitary matrices each, S E,N for the left-handed and T E,N for the righthanded fields. The mixing angles in the right-handed sector are suppressed compared to the right-handed ones by the ratio of the light fermion masses versus the mass M 1 , therefore their contribution to the phenomenology can be neglected.…”

“…The mixing angles in the right-handed sector are suppressed compared to the right-handed ones by the ratio of the light fermion masses versus the mass M 1 , therefore their contribution to the phenomenology can be neglected. Furthermore, the couplings of the new states to the SM ones only depends on two vectors in flavor:Interesting relations between the couplings and masses have already been derived in [17], so in this section we will limit ourselves to study in more detail some interesting limits in order to clarify important properties of the new leptons.Firstly, the masses of the SM leptons are typically much smaller than the mass M 1 , so we can start by neglecting their effect, i.e. setting m i 1 = m i 2 = 0.…”

“…We can see that these productions of the exotic leptons have sizable rates, because they are produced via the standard model electro-weak gauge interaction and they are not suppressed by mixing angels. Single production in association with a SM lepton, being proportional to λ, is always negligibly small [17].In the following we will discuss the most promising channels for the discovery of the exotic leptons, focusing on a 14 TeV LHC run. We chose this center of mass energy mainly to be able to compare our results with the ones in [17], knowing that the next LHC run will likely be at a lower energy of 12.5 or 13 TeV.…”

“…Single production in association with a SM lepton, being proportional to λ, is always negligibly small [17].…”

Is there really aW→τνpuzzle?

“…Such exotic leptons were examined in Ref. [25], and were allowed to mix with all three flavors of SM leptons. This then generates flavorchanging neutral-current processes (FCNCs) such as µ → eγ, τ → µµµ, etc.…”