M.B. Gavela

Large gauge invariant non-standard neutrino interactions

Theories beyond the standard model must necessarily respect its gauge symmetry. This implies strict constraints on the possible models of nonstandard neutrino interactions, which we analyze. The focus is set on the effective low-energy dimension six and eight operators involving four leptons, decomposing them according to all possible tree-level mediators, as a guide for model building. The new couplings are required to have sizable strength, while processes involving four charged leptons are required to be suppressed. For nonstandard interactions in matter, only diagonal tau-neutrino interactions can escape these requirements and can be allowed to result from dimension six operators. Large nonstandard neutrino interactions from dimension eight operators alone are phenomenologically allowed in all flavor channels and are shown to require at least two new mediator particles. The new couplings must obey general cancellation conditions both at the dimension six and dimension eight levels, which result from expressing the operators obtained from the mediator analysis in terms of a complete basis of operators. We illustrate with one example how to apply this information to model building.

μ→Eγ and τ→lγ decays in the fermion triplet seesaw model

In the framework of the seesaw models with triplets of fermions, we evaluate the decay rates of

Disentangling a dynamical Higgs

\mu \to e \gamma

Anomalous Higgs couplings at the LHC, and their theoretical interpretation

and

Flavor with a light dynamical "Higgs particle"

\tau \to l \gamma

Dark Coupling and Gauge Invariance

transitions. We show that although, due to neutrino mass constraints, those rates are in general expected to be well under the present experimental limits, this is not necessarily always the case. Interestingly enough, the observation of one of those decays in planned experiments would nevertheless contradict bounds stemming from present experimental limits on the

The neutrino factory: Beam and experiments

\mu \to eee

E1 Working Group Summary: Neutrino factories and muon colliders

and

Fading of symmetry nonrestoration at finite temperature

\tau \to 3 l

Erratum: dark coupling

decay rates. Such detection of radiative decays would therefore imply that there exist sources of lepton flavour violation not associated to triplet fermions.