2026/07/27 by Claudia Cornella, Max Ferré, Matthias König +1
#hep-ph
Using a sequence of effective field theories (EFTs), we calculate the rate for the leptonic decay B-→τ-ντ(γ) including real and virtual QED corrections, with a cut E\rm cut≪Λ\rm QCD imposed on electromagnetic radiation in the B-meson rest frame. We establish a factorization theorem for the rate and evaluate it at O(α), resumming the leading logarithmic corrections to all orders in perturbation theory. The large mass mτ allows us to treat the tau lepton as a heavy fermion below μ∼ mB∼ mτ, leading to an EFT construction that is structurally different and noticeably simpler than that for the muon case. In particular, hadron-structure dependent QED corrections can be described in terms of QED-induced B-→τ- form factors, which should be calculable on the lattice. Our analysis includes the leading Λ\rm QCD/mτ corrections as well as the leading corrections in E\rm cut/Λ\rm QCD. We show that contributions of the form Λ\rm QCDmB/mτ2, which are naively sizable, cancel among each other. Contrary to the muon channel, structure-dependent corrections involving BB^∗γ transitions are numerically negligible for the tau case. The remaining logarithmic dependence on Ecut is mild. We estimate that the present uncertainty in the calculation of the structure-dependent QED corrections is about 0.5% of the rate. As a byproduct, we present a state-of-the-art prediction for the lepton flavor universality ratio of the tau and muon channels.