Semileptonic b → c transitions, and in particular the ratios R(, can be used to test the universality of the weak interactions. In light of the recent discrepancies between the experimental measurements of these observables by BaBar, Belle and LHCb and the Standard Model predicted values, we study the robustness of the latter. Our analysis reveals that R(D) might be enhanced by lepton mass effects associated to the mostly unknown scalar form factor. In constrast, the Standard Model prediction for R(D * ) is found to be more robust, since possible pollutions from B * contributions turn out to be negligibly small, which indicates that R(D * ) is a promising observable for searches of new physics.

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We calculate the ratios Rτ/P≡ Γ (τ → Pντ [γ]) /Γ (P → μνμ [γ]) (P = π, K) at one loop following a large-NC expansion where Chiral Perturbation Theory is enlarged by including the lightest resonances and respecting the short-distance behavior dictated by QCD. We find δRτ/π = (0.18 ± 0.57)% and δRτ/K = (0.97 ± 0.58)%, where the uncertainties are induced fundamentally by the counterterms. We test the lepton universality, obtaining |gτ/gμ|π = 0.9964 ± 0.0038 and |gτ/gμ|K = 0.9857 ± 0.0078, and analyze the CKM unitarity, getting results at 2.1σ and 1.5σ from unitarity via |Vus/Vud| and |Vus|, respectively. We also update the search for non-standard interactions in τ decays. As a by-product, we report the theoretical radiative corrections to the τ → Pντ [γ] decay rates: δτπ = −(0.24 ± 0.56)% and δτK = −(0.15 ± 0.57)%.

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We study flavor violating processes in the production or decay of a neutral pseudoscalar meson P 0 in the framework of a type III two Higgs Doublet Model with four-texture Yukawa couplings. We use a version of the model where Yukawa interactions of neutral Higgs bosons allow for flavor change at the tree-level, but conserves CP symmetry. The physical Yukawa couplings respect CP-invariance due to the Hermiticity conditions that we impose on the fermion mass matrices. We focus on all possible τ ± → l ± P 0 and P 0 → l + l ′− decay channels, where l, l ′ are charged leptons. We find that these processes provide complementary information on quark and lepton FCNC Yukawa couplings. In particular flavor violating parameters in the quark sector, χ sb and χ db , are significantly constrained by present experimental data, whereas the corresponding parameters in the leptonic sector are less constrained.

The disappearance searching experiments x     use charged current quasielastic (CCQE) reaction to detect an arriving neutrino and reconstruct its energy, while the CC1π + production can mimic the CCQE signal process. In e     appearance experiments, the NC1π 0 production process can lead to a fake e  event by the impossibility for the detector of distinguish an arriving electron or a photon. Here we present a consistent model, from the point of view of the construction of the elemental amplitude, for the mentioned pion production background processes including bounding, smearing and final state interaction (FSI) effects in a single fashion. Results are comparable with more evolved approaches based on Monte Carlo simulations.

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