Abstract
We study the impact of heavy vector-like leptons on several observables in collider and low-energy physics. These states, present in many well-motivated extensions of the Standard Model, can induce lepton flavour violation and non-standard Higgs decays. We study these effects in an effective model inspired by the composite Higgs scenario. After deriving bounds on the mass and production cross-section of the vector-like states using recent LHC data on multilepton searches, we discuss the modification of the Higgs decays to dilepton, diphoton and $Z\gamma$ final states as well as low-energy observables like radiative lepton decays, the anomalous magnetic moment of the muon and the electric dipole moment of the electron. We find several interesting correlations. In particular, we show that branching fractions of lepton flavour-violating Higgs decays at an observable level are prohibited due to the strong bounds on the radiative lepton decays.
Highlights
We explore the phenomenology of vector-like leptons on several fronts
We put a special focus on the lepton flavour violating (LFV) Higgs decays h → eiej, that are a good example of LFV at colliders, a possibility less explored than LFV at low-energy experiments
We have explored the phenomenology of a simple model with vector-like leptons, with detailed studies of their impact on lepton flavour violation, Higgs decays and collider physics
Summary
In this paper we are interested in the class of models where the masses of SM charged leptons are generated via mixing with heavy vector-like leptons. The chiral leptons do not acquire mass directly, but only via the mixing with the vector-like leptons: Lmix = MlLλlLR + ELλeeR + h.c. Here λi are 3 × 3 matrices in the generation space. By choosing hierarchical λ’s it is possible to generate hierarchies of lepton masses and mixings, even if the Yukawa couplings are anarchic. Dirac and Majorana neutrino masses and be introduced in this way, see [8, 9, 11, 26] Since extensions in this direction do not have any impact on charged lepton flavour violation, we choose not to discuss this issue any further
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