Abstract
We analyzed how to test flavor and helicity structures of the corresponding amplitudes in view of future data, motivated by the recent hints of lepton flavor universality violation observed in semileptonic B decays. The general assumption that non-standard effects are controlled by a U(2)5 flavor symmetry, minimally broken as in the Standard Model Yukawa sector, leads to stringent predictions on leptonic and semileptonic B decays. Future measurements will allow to prove or falsify this general hypothesis independently of its dynamical origin.
Highlights
The current data collected by LHCb, BaBar and Belle experiments exhibit intriguing hints of violations of Lepton Flavor Universality (LFU) both in charged-current [2,3,4,5,6] and neutral-current [7,8,9,10,11,12] semileptonic B decays, and it gets attention as B-anomalies
In the context of the recent anomalies, we adopt the general assumptions that the NP effects are controlled by U(2)5 flavor symmetry, which is a useful organizing principle to address the flavor hierarchies in the Standard Model (SM) [13,14,15]
It is a global symmetry that the SM Lagrangian satisfies in good approximation; in the limit where we neglect all entries in the Yukawa couplings but for third generation masse, and given as
Summary
The current data collected by LHCb, BaBar and Belle experiments exhibit intriguing hints of violations of Lepton Flavor Universality (LFU) both in charged-current [2,3,4,5,6] and neutral-current [7,8,9,10,11,12] semileptonic B decays, and it gets attention as B-anomalies. The features of the hypothetical NP should have dominant couplings to third generation fermions and smaller couplings to second generation fermions This non-trivial flavor structure resembles the observed flavor hierarchies in the Standard Model (SM) Yukawa couplings, and the possibility of a common explanation for these phenomena is opened. Under the U(2) flavor symmetry, the right handed light fermion operators are suppressed and this feature reduces the number of relevant semileptonic operators. +(2 CS Λ[Si jαβ] O edq + h.c.) , where CVi,S control the overall strength of the NP effects and ΛVi,S are tensors that parametrize the flavor structure. They are normalized by setting Λ[V3i3,S33] = 1, which is the only term surviving in the exact U(2) limit. Scalar operators with light fermions suppressed by factor ms/mb and mμ/mτ
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