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arXiv · 1606.00524

Revisiting Lepton Flavour Universality in B Decays

Ferruccio Feruglio·Paride Paradisi·Andrea Pattori
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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.

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Ferruccio Feruglio, Paride Paradisi, Andrea Pattori. 2016-12-14. Revisiting Lepton Flavour Universality in B Decays. https://doi.org/10.1103/physrevlett.118.011801

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