B meson anomalies and large B⁺→ K⁺ν ν̄ in non-universal U(1)′ models

A bstract In view of both the latest LHCb measurement of R_K( ) R K ∗ and the new 2 . 7 σ deviation reported by Belle II on B⁺→ K⁺ν ν̄ B + → K + ν ν ¯ decays, we present a fit to the B meson anomalies for various one and two dimensional hypothesis including complex Wilson coefficients. We show in a model-independent way that the generic non-universal U(1) ′ extensions of the SM, without flavour violation, fail to simultaneously fit those observables and corroborate that they can modify BR(B⁺→ K⁺ν ν̄) BR B + → K + ν ν ¯ up to only a 10%. In view of this deficit, we propose a new way in which those models can accommodate the data at tree level by introducing lepton flavour violating couplings and non-diagonal elements of the charged lepton mixing matrix, with implications in future charged lepton flavour violation searches.