title: Revisiting Lepton Flavor Universality in B Decays.
abstract: Lepton flavor universality (LFU) in B decays is revisited by considering a class of semileptonic operators defined at a scale Λ above the electroweak scale v. The importance of quantum effects, so far neglected in the literature, is emphasized. We construct the low-energy effective Lagrangian taking into account the running effects from Λ down to v through the one-loop renormalization group equations (RGEs) in the limit of exact electroweak symmetry and QED RGEs from v down to the 1 GeV scale. The most important quantum effects turn out to be the modification of the leptonic couplings of the vector boson Z and the generation of a purely leptonic effective Lagrangian. Large LFU breaking effects in Z and τ decays and visible lepton flavor violating effects in the processes τ→μℓℓ, τ→μρ, τ→μπ, and τ→μη^{(')} are induced.
authors.affiliation: Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, I-35100 Padova, Italy.|Istituto Nazionale Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italy.
authors.forename: Ferruccio
authors.initials: F
authors.lastname: Feruglio
authors.affiliation: Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, I-35100 Padova, Italy.|Istituto Nazionale Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italy.
authors.forename: Paride
authors.initials: P
authors.lastname: Paradisi
authors.affiliation: Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, I-35100 Padova, Italy.|Physik-Institut, Universität Zürich, CH-8057 Zürich, Switzerland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Pattori