Abstract
We investigate whether the 2.6σ deviation from lepton flavour universality in B+→K+ℓ+ℓ− decays recently observed at the LHCb experiment can be explained in minimal composite Higgs models. We show that a visible departure from universality is indeed possible if left-handed muons have a sizable degree of compositeness. Constraints from Z-pole observables are avoided by a custodial protection of the muon coupling.
Highlights
Rare B meson decays based on the quark-level transition b → s + −, with = e, μ, τ, are sensitive probes of physics beyond the Standard Model (SM) as these flavour-changing neutral currents are loop and CKM suppressed in the SM
It has been demonstrated already that in models where the b → s + − transition is mediated at the tree level by a heavy neutral gauge boson [2,3,4,5,6,7,8] or by spin-0 or spin-1 leptoquarks [3, 9,10,11,12], it is possible to explain the measurement without violating other constraints
We have demonstrated that a departure from lepton flavour universality in B+ → K+ + − decays, as hinted by the recent LHCb measurement, could be explained in minimal composite Higgs models if left-handed muons have a sizable degree of compositeness
Summary
In composite Higgs models, which at present arguably constitute the most compelling solution to the hierarchy problem next to supersymmetry, one interesting possibility recently considered to explain (1) is to postulate the presence of composite leptoquarks [13]. This comes at the price of a significant complication of the models. In more minimal models a thorough analysis of the possible size of LFU violation is
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