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

A bstract In view of both the latest LHCb measurement of R₊^ () R K ∗ and the new 2. 7 σ deviation reported by Belle II on B^+ K^+ 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^+) 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.