This chapter of the report of the "Flavor in the era of the LHC" Workshop discusses the theoretical, phenomenological and experimental issues related to flavor phenomena in the charged lepton sector and in flavor conserving CPviolating processes. We review the current experimental limits and the main theoretical models for the flavor structure of fundamental particles. We analyze the phenomenological consequences of the available data, setting constraints on explicit models beyond the standard model, presenting benchmarks for the discovery potential of forthcoming measurements both at the LHC and at low energy, and exploring options for possible future experiments.

The minimal SU(5) theory augmented by the fermionic adjoint representation restores the coupling constant unification and gives realistic neutrino masses and mixing through the hybrid Type I and Type III seesaw. The crucial prediction of the theory is an SU(2) lepton triplet with the mass below TeV. We study the signature of these heavy leptons and propose the strategy to test this mechanism at the hadron and lepton colliders. The smoking gun evidence of the theory is ∆L = 2 lepton number violation through events of a pair of like-sign leptons plus four jets without significant missing energy at hadron colliders. We find that via this unique channel, the heavy lepton can be searched for up to a mass of 200 GeV at the Tevatron with 8 fb −1 , and up to 450 (700) GeV at the LHC of 14 TeV C.M. energy with 10 (100) fb −1 . The signal rate at the 10 TeV LHC is reduced to 60% − 35% for a mass of 200−700 GeV. We also comment on how to distinguish this theory from other models with similar heavy leptons. Finally, we compare the production rates and angular distributions of heavy leptons in e + e − collisions for various models.

We study the vacuum stability and unitarity conditions for a 125 GeV Standard Model (SM)-like Higgs boson mass in the type-II seesaw model. We find that, as long as the seesaw scale is introduced below the SM vacuum instability bound, there exists a large parameter space predicting a 125 GeV Higgs mass, irrespective of the exact value of the seesaw scale, satisfying both stability and unitarity conditions up to the Planck scale. We also study the model predictions for the Higgs partial decay widths in the diphoton and Z+photon channels with respect to their SM expectations and find that the decay rates for these two processes are correlated. We further show that for any given enhancement in the Higgs-to-diphoton rate over its SM expectation, there exists an upper bound on the type-II seesaw scale, and hence, on the masses of the associated doubly-and singly-charged Higgs bosons in the allowed parameter space. For instance, if more than 10% enhancement persists in the Higgs-to-diphoton channel, the upper limit on the type-II seesaw scale is about 450 GeV which is completely within the reach of the 14 TeV LHC. We believe this to be an encouraging result for the experimental searches of the singly-and doubly-charged Higgs bosons which, in combination with improved sensitivity in the Higgs-to-diphoton and Higgs-to-Z+photon channels, could probe the entire allowed parameter space of the minimal type-II seesaw model, and establish/eliminate it as a single viable extension of the SM.

We investigate how far a new physics scenario affecting primarily the third-generation fermions can ameliorate the tension between B decay observables and Standard Model expectations. Adopting a modelindependent approach, we find that among the three observables that show signs of such a tension, viz., the branching fractions for B þ ! , B d ! DðD Ã Þ, and the like-sign dimuon anomaly in neutral B decays, the first two can be explained adequately, while there is only a marginal improvement for the third. As a spin-off, it is shown that one can also accommodate a change in the branching fraction of the Higgs boson to a lepton pair from the Standard Model expectation, if such a change is established in future data.

Recently a new mechanism has been proposed to cure the problem of fermion mass hierarchy in the Standard Model (SM) model. In this scenario, all SM charged fermions other than top quark arise from higher dimensional operators involving the SM Higgs field. This model also predicted some interesting phenomenology of the Higgs boson. We generalize this model to accommodate neutrino masses (Dirac & Majorana) and also obtain the mixing pattern in the leptonic sector. To generate neutrino masses, we add extra three right handed neutrinos $(N_{iR})$ in this model.Comment: 20 pages, the content on results and phenomenology have been expanded, a new section on UV completion of the model has been added and also some new references, this version has been accepted by Physical Review