B-decay discrepancies after Moriond 2019

Following the updated measurement of the lepton flavour universality (LFU) ratio RK in B. K decays by LHCb, as well as a number of further measurements, e.g. RK* by Belle and Bs. mu mu by ATLAS, we analyse the global status of new physics in b. s transitions in the weak effective theory at the b-quark scale, in the Standard Model effective theory above the electroweak scale, and in simplified models of new physics. We find that the data continues to strongly prefer a solution with new physics in semileptonic Wilson coefficients. A purely muonic contribution to the combination C9 = -C10, well suited to UV-complete interpretations, is now favoured with respect to a muonic contribution to C9 only. An even better fit is obtained by allowing an additional LFU shift in C9. Such a shift can be renormalization-group induced from four-fermion operators above the electroweak scale, in particular from semi-tauonic operators, able to account for the potential discrepancies in b. c transitions. This scenario is naturally realized in the simplified U1 leptoquark model. We also analyse simplified modelswhere a LFU effect in b. s is induced radiatively from four-quark operators and show that such a setup is on the brink of exclusion by LHC di-jet resonance searches.