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

Abstract

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)%.

Radiative corrections and new physics tests in semileptonic tau decays

“…finding [33,34] δ τ π = −(0.24±0.56)% and δ τ K = −(0.15± 0.57)%. Now, application of the radiative corrections highlighted in red in Eqs.…”

“…[36,37]) and the latter was studied only recently, in Refs. [33,34]. We will not dwell here into the details of the computation of δ τ P | vSD [33,34].…”

“…[33,34]. We will not dwell here into the details of the computation of δ τ P | vSD [33,34]. Suffice it to say that they depend on three (one vector-and two axial-current) form factors.…”

Exclusive hadronic $τ$ decays, within $\&$ beyond the Standard Model

“…, which is obtained from lattice data [10]. Radiative corrections (including structuredependent effects) are essential in elucidating this [11][12][13]. LEP measurements of this one-meson tau decays branching ratios [14,15] and by BaBar of their normalization with respect to the lepton 1 See, respectively, Gabriel López Castro ( † ), Alberto Lusiani ( * ), Bachir Moussallam ( • ), Zhi-Hui Guo and Frederic Noël ( ), Álex Miranda ( % ), Fabian Krinner and Mikhail Mikhasenko ( △ ) talks and corresponding contributions to these proceedings.…”

“…(with great focus on the CP asymmetry in K S π − [81-85]), Kη (′) [86] and a joint analysis of all one-and two-meson tau decays [87], recently updated using improved radiative corrections for the (π/K) − modes [13].…”