Explaining the R_K and R_K^* anomalies

Recent LHCb results on R_K*, the ratio of the branching fractions of B → K*μ⁺μ^- to that of B → K*e⁺e^-, for the dilepton invariant mass bins q² ≡ m_ll² = [0.045-1.1] GeV² and [1.1-6] GeV² show approximately 2.5σ deviations from the corresponding Standard Model prediction in each of the bins. This, when combined with the measurement of R_K (q² = [1-6] GeV²), a similar ratio for the decay to a pseudo-scalar meson, highly suggests lepton non-universal new physics in semi-leptonic B meson decays. In this work, we perform a model independent analysis of these potential new physics signals and identify the operators that do the best job in satisfying all these measurements. We show that heavy new physics, giving rise to q² independent local 4-Fermi operators of scalar, pseudo-scalar, vector or axial-vector type, is unable to explain all the three measurements simultaneously, in particular R_K* in the bin [0.045-1.1], within their experimental 1σ regions. We point out the possibility to explain R_K* in the low bin by an additional light (<or similar 20 MeV) vector boson with appropriate coupling strengths to (anti bs) and (anti ee). (orig.)