We evaluate the model-dependent piece of O(α) long-distance radiative corrections to τ − → π − π 0 ντ decays by using a meson dominance model. We find that these corrections to the di-pion invariant mass spectrum are smaller than in previous calculations based on chiral perturbation theory. The corresponding correction to the photon inclusive rate is tiny (−0.15%) but it can be of relevance when new measurements reach better precision.

The long-distance electromagnetic radiative corrections to τ − → π − π 0 ντ are re-evaluated. A meson dominance model is used to describe the emission of real photons in this decay. Results obtained for the hadronic spectrum and the decay rate in photon inclusive reactions are compared with previous calculations based on the chiral resonance theory. Independent tests in τ → ππνγ that can help to validate the predictions of one of the two models are briefly discussed.

We consider the bremsstrahlung and model-dependent contributions to the radiative decay τ − → π − π 0 ντ γ in the context of a meson dominance model. We focus on several observables related to this decay, including the branching ratio and the photon and di-pion spectra. Particular attention is paid to the sensitivity of different observables upon the effects of model-dependent contributions and of the magnetic dipole moment of the ρ − (770) vector meson. Important numerical differences are found with respect to results obtained in the framework of chiral perturbation theory.

The one-loop contribution of the excited Kaluza-Klein (KK) modes of the SUL(2) gauge group on the off-shell W − W + γ and W − W + Z vertices is calculated in the context of a pure Yang-Mills theory in five dimensions and its phenomenological implications discussed. The use of a gauge-fixing procedure for the excited KK modes that is covariant under the standard gauge transformations of the SUL(2) group is stressed. A gauge-fixing term and the Faddeev-Popov ghost sector for the KK gauge modes that are separately invariant under the standard gauge transformations of SUL(2) are presented. It is shown that the one-loop contributions of the KK modes to the off shell W − W + γ and W − W + Z vertices are free of ultraviolet divergences and well-behaved at high energies. It is found that for a size of the fifth dimension of R −1 ∼ 1 TeV, the one-loop contribution of the KK modes to these vertices is about one order of magnitude lower than the corresponding standard model radiative correction. This contribution is similar to the one estimated for new gauge bosons contributions in other contexts. Tree-level effects on these vertices induced by operators of higher canonical dimension are also investigated. It is found that these effects are lower than those generated at the one-loop order by the KK gauge modes.

A comprehensive analysis of the lepton flavor violating (LFV) decays Z → ℓ ∓ i ℓ ± j is presented within the effective Lagrangian approach. Both the decoupling and nondecoupling scenarios are explored. The experimental constraints from ℓi → ℓjℓ k lk and ℓi → ℓjγ as well as some relationships arising from the gauge invariance of the effective Lagrangian are used to put constraints on Z → ℓ ∓ i ℓ ± j . It is found that while current experimental data impose very strong constraints on Z → µ ∓ e ± , the channel Z → τ ∓ ℓ ± still may be at the reach of the planned TESLA collider.