One-loop determination of τ → π(K)ντ [γ] branching ratios and new physics tests

A bstract We calculate the ratios R τ / P ≡ Γ ( → Pν [ γ ]) /Γ μν μ = π , K ) at one loop following a large- N C expansion where Chiral Perturbation Theory is enlarged by including lightest resonances and respecting short-distance behavior dictated QCD. find δR (0 . 18 ± 0 57)% 97 58)%, uncertainties are induced fundamentally counterterms. test lepton universality, obtaining | g 9964 0038 9857 0078, analyze CKM unitarity, getting results 2 1 σ 5 from unitarity via V us ud |, respectively. also update search for non-standard interactions in decays. As by-product, we report theoretical radiative corrections to ] decay rates: δ τπ − 24 56)% τK 15 57)%.