Z′ model for b→sℓℓ¯ flavor anomalies

We study the implications of flavor-changing neutral currents (FCNC's) in a model with the SU(2)_l×SU(2)_h×U(1)_Y electroweak gauge symmetry for several anomalies appearing in b→sℓℓ¯ induced B decays in LHCb data. In this model, SU(2)_l and SU(2)_h govern the left-handed fermions in the first two generations and the third generation, respectively. The physical Z and Z′ generate the b→sℓℓ¯ transition at tree level, leading to additional contributions to theb→sℓℓ¯ semileptonic operators O_9,10. We find that although B_s-B_s mixing constrains the parameters severely, the model can produce values of C_9,10^NP in the range determined by Descotes-Genon et al. (Global analysis of b→sℓℓ¯ anomalies, arXiv:1510.04239) for this scenario to improve the global fit of observables in decays induced by the b→sμμ transition. The Z′  boson in this model also generates tree-level FCNC's for the leptonic interactions that can accommodate the experimental central value of R_K=B(B→Kμμ)/B(B→Keē)=0.75. In this case, the model predicts sizable branching ratios for B→Keτ, B→Kτē, and an enhancement of B→Kττ with respect to its standard model value.