RK(⁎) and R(D(⁎)) anomalies resolved with lepton mixing

In a recent paper [1], we had advanced a minimal resolution of some of the persistent anomalies in semileptonic B-decays. These include the neutral-current observables RK and RK⁎, as well as the charged-current observables R(D) and R(D⁎). Recently, it has been observed that the semileptonic decays of the Bc meson also hint at a similar type of anomaly. In this longer version, we discuss in detail why, if the anomalies are indeed there, it is a challenging task to explain the data consistently in terms of a simple and compelling new physics scenario. We find that the minimal scheme to achieve a reasonable fit involves the inclusion of just two (or, at worst, three with a possible symmetry relationship between their Wilson coefficients) new current-current operators, constructed in terms of the flavour eigenstates, augmented by a change of basis for the charged lepton fields. With only three unknown parameters, this class of models not only explain all the anomalies (including that in Bc→J/ψℓν) to a satisfactory level but also predict some interesting signatures, like B→Kμτ, Bs→ττ, B→K plus missing energy, or direct production of τ+τ−, that can be observed at LHCb or Belle-II.