B-decays: Anomalies and Challenges

Several tensions between SM predictions and data in b→s transitions persist since the LHCb measurements of the B→K⋆μμ angular distribution in 2013. There has been plenty of debate about the role of hadronic uncertainties and around ∼ 200 papers trying to explain such tensions with NP, both model-independently and within NP models. To this set of tensions one must add the hint for lepton-flavor non-universality in RK, which is surprisingly compatible with the previous tensions if one assumes NP couples only to muons. This cannot be explained with hadronic effects. One might then speculate that the same new physics is responsible for the long standing tensions in the b→cℓν observables R(D(⋆)), due to the SU(2)L invariance of the underlying dynamics if the new physics scale is above the EW scale. Lepton-flavor universality also suggests a possible correlation to lepton-flavor violation. All this is model-dependent, but if these tensions are confirmed, the panorama is bright. Such large new physics effects also suggests that one should start paying attention to operator-mixing effects, since there are, on the other hand, extremely tight constraints on flavor-non-universality from tau decays. Correlations to collider observables are also very relevant.