The flavor of a minimal composite S1 leptoquark and the b→cτν anomaly

Abstract

Several experiments have measured a deviation in B → D(∗) semileptonic decays, that point to new physics at the TeV scale violating lepton flavor universality. A scalar leptoquark S1, with a suitable structure of couplings in flavor space, is known to be able to solve this anomaly modifying b → cτν̄. In the context of composite Higgs models, we consider a theory containing H and S1 as Nambu-Goldstone bosons (NGBs) of a new strongly interacting sector, with ordinary resonances at a scale O(10) TeV. Assuming anarchic partial compositeness of the Standard Model (SM) fermions we calculate the potential of the NGBs that is dominated by the fermions of the third generation, we compute RD(∗) and estimate the corrections to flavor observables by the presence of S1. We find that the SM spectrum and mS1 ∼ TeV can be obtained with a NGB decay constant of order ∼ 5 TeV. We obtain a robust correlation between the main corrections to RD(∗), B K(∗)νν and gτ/gµ , that leads to a sever bound on RD(∗), roughly 2σ belowthe experimental value. Besides the bounds on the flavor observables gτW, BR(τ → µγ) and ∆mBs are saturated, with the first one requiring a coupling between resonances g∗≲ 2, whereas the second one demands mS1 ≳ 1.7 TeV, up to corrections of O(1).