Flavour anomalies after the RK∗ measurement

The LHCb measurement of the μ/e ratio RK∗ indicates a deficit with respect to the Standard Model prediction, supporting earlier hints of lepton universality violation observed in the RK ratio. We show that the RK and RK∗ ratios alone constrain the chiralities of the states contributing to these anomalies, and we find deviations from the Standard Model at the 4σ level. This conclusion is further corroborated by hints from the theoretically challenging b → sμ+μ− distributions. Theoretical interpretations in terms of Z′, lepto-quarks, loop mediators, and composite dynamics are discussed. We highlight their distinctive features in terms of the chirality and flavour structures relevant to the observed anomalies.