Computing one-loop radiative corrections in τ → π(K)ν[γ] and testing new physics

Abstract

Without a doubt the ratios Rτ/p = Γ(τ → Pντ[γ])/Γ(P → μνμ[γ]) (P = π, K) give a convenient scenario to test the lepton universality, the CKM unitarity and to search for non-standard interactions in τ decays. Moreover, the previous theoretical estimation of these observables is more than twenty-five years old and some assumptions of that estimation are unrealistic. Therefore, an update of Rτ/P was timely. The one-loop radiative corrections have been computed by considering an expansion of Chiral Perturbation Theory including the lightest spin-one resonances and respecting the short-distance behavior dictated by QCD. We have reported δRτ/π = (0.18±0.57)% and δRτ/K = (0.97±0.58)%, where the uncertainties have been induced fundamentally by the estimation of the counterterms. We have tested the lepton universality, the CKM unitarity and have searched for new physics in τ decays. As a by-product, we have also determined the theoretical radiative corrections to the τ → Pντ[γ] decay rates, δτπ = —(0.24 ± 0.56)% and δτK = —(0.15 ± 0.57)%.