Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement

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The vector leptoquark representation, Uµ = (3, 1, 2/3), was recently identified as an exceptional single mediator model to address experimental hints on lepton flavour universality violation in semileptonic B-meson decays, both in neutral (b → sµµ) and charged (b → cτ ν) current processes. Nonetheless, it is well-known that massive vectors crave an ultraviolet (UV) completion. We present the first full-fledged UV complete and calculable gauge model which incorporates this scenario while remaining in agreement with all other indirect flavour and electroweak precision measurements, as well as, direct searches at high-pT . The model is based on a new non-abelian gauge group spontaneously broken at the TeV scale, and a specific flavour structure suppressing flavour violation in ∆F = 2 processes while inducing sizeable semileptonic transitions.

We attempt to explain recent anomalies in semileptonic B decays at LHCb via a composite Higgs model, in which both the Higgs and an SU(2) L -triplet leptoquark arise as pseudo-Goldstone bosons of the strong dynamics. Fermion masses are assumed to be generated via the mechanism of partial compositeness, which largely determines the leptoquark couplings and implies non-universal lepton interactions. The latter are needed to accommodate tensions in the b → sµµ dataset and to be consistent with a discrepancy measured at LHCb in the ratio of B + → K + µ + µ − to B + → K + e + e − branching ratios. The data imply that the leptoquark should have a mass of around a TeV. We find that the model is not in conflict with current flavour or direct production bounds, but we identify a few observables for which the new physics contributions are close to current limits and where the leptoquark is likely to show up in future measurements. The leptoquark will be pair-produced at the LHC and decay predominantly to third-generation quarks and leptons, and LHC13 searches will provide further strong bounds.