Revisiting Lepton Flavour Universality in B Decays
Abstract
Lepton flavour universality (LFU) in B-decays is revisited by considering a class of semileptonic operators defined at a scale Lambda above the electroweak scale v. The importance of quantum effects, so far neglected in the literature, is emphasised. We construct the low-energy effective Lagrangian taking into account the running effects from Lambda down to v through the one-loop renormalization group equations (RGE) 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 tau decays and visible lepton flavour violating (LFV) effects in the processes tau -> mu ll, tau -> mu rho, tau -> mu pi and tau -> mu eta^(') are induced.
Cite
@article{arxiv.1606.00524,
title = {Revisiting Lepton Flavour Universality in B Decays},
author = {Ferruccio Feruglio and Paride Paradisi and Andrea Pattori},
journal= {arXiv preprint arXiv:1606.00524},
year = {2017}
}
Comments
5 pages, 2 figures. V2: Minor text improvements. Published PRL version