Implications of Lepton Flavor Universality Violations inBDecays

Abstract

Present measurements of b→cτν and b→uτν transitions differ from the standard model predictions of lepton flavor universality by almost 4σ. We examine new physics interpretations of this anomaly. An effective field theory analysis shows that minimal flavor violating models are not preferred as an explanation, but are also not yet excluded. Allowing for general flavor violation, right-right vector and right-left scalar quark currents are identified as viable candidates. We discuss explicit examples of two Higgs doublet models, leptoquarks as well as quark and lepton compositeness. Finally, implications for LHC searches and future measurements at the (super-)B factories are presented.

Status of B to D(*) τ ν decays in two-Higgs-doublet models

“…In order to avoid the ambiguity in the determination of |V ub |, it is convenient to consider the ratio [13] …”

“…It was first found in Ref. [13] that none of the 2HDMs with natural flavour conservation (NFC) can simultaneously accommodate the current measurements of the three ratios {R(D), R(D * ), R π τ/ }. To accommodate the experimental data on tauonic-B decays: B → D ( * ) τν and B → τν, one has to allow for a more general Yukawa structure as provided by the Yukawa alignment hypothesis (A2HDM) or by assuming the presence of tree-level FCNCs [14].…”

Revisiting Lepton Flavour Universality in B Decays

“…Conclusions Recent experimental data hinting at non-standard LFU breaking effects in semileptonic Bdecays [1-3, 5] stimulated many theoretical investigations of NP scenarios [7][8][9][10][11][12][13][14][15][16][17]27]. In this work, we revisited LFU in B-decays assuming a class of gauge invariant semileptonic operators at the NP scale Λ v, as in Refs.…”

“…Such a program has not been carried out in the literature so far and it has significant implications on the conclusions of Refs. [11][12][13][14][15][16][17]. 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.…”

“…[11][12][13][14][15][16][17]. The main new development of our study is the construction of the low-energy effective Lagrangian taking into account the running of the Wilson coefficients of a suitable operator basis and the matching conditions when mass thresholds are crossed.…”