Flavour anomalies after the $R_{K^*}$ measurement

Preprint number: CP3-Origins-2017-14 DNRF90
Authors: Guido D’Amico (Theoretical Physics Department, CERN, Geneva, Switzerland), Marco Nardecchia (Theoretical Physics Department, CERN, Geneva, Switzerland), Paolo Pandi (Theoretical Physics Department, CERN, Geneva, Switzerland), Francesco Sannino (Theoretical Physics Department, CERN, Geneva, Switzerland & CP3-Origins & DIAS), Alessandro Strumia (Theoretical Physics Department, CERN, Geneva, Switzerland & Pisa University), Riccardo Torre (Theoretical Particle Physics Laboratory, Institute of Physics, EPFL, Lausanne, Switzerland), and Alfredo Urbano (Theoretical Physics Department, CERN, Geneva, Switzerland)
External link: arXiv.org

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The LHCb measurement of the $\mu/e$ ratio $R_{K^*}$ indicates a deficit with respect to the Standard Model prediction, supporting earlier hints of lepton universality violation observed in the $R_K$ ratio. We show that the $R_K$ and $R_{K^*}$ ratios alone constrain the chiralities of the states contributing to these anomalies, and we find deviations from the Standard Model at the $4\sigma$ level. This conclusion is further corroborated by hints in the theoretically challenging $b\to s\mu^+\mu^-$ distributions. Theoretical interpretations in terms of $Z’$, lepto-quarks, loop mediators, and composite dynamics are discussed. We highlight their distinctive features in terms of chiralities and flavour structure relevant for the observed anomalies.