Updated Bs -mixing constraints on new physics models for b →s+ - Anomalies

Many new physics models that explain the intriguing anomalies in the b-quark flavor sector are severely constrained by Bs mixing, for which the Standard Model prediction and experiment agreed well until recently. The most recent Flavour Lattice Averaging Group (FLAG) average of lattice results for the nonperturbative matrix elements points, however, in the direction of a small discrepancy in this observable Cabibbo-Kobayashi-Maskawa (CKM). Using up-to-date inputs from standard sources such as PDG, FLAG and one of the two leading CKM fitting groups to determine ΔMsSM, we find a severe reduction of the allowed parameter space of Z′ and leptoquark models explaining the B anomalies. Remarkably, in the former case the upper bound on the Z′ mass approaches dangerously close to the energy scales already probed by the LHC. We finally identify some model-building directions in order to alleviate the tension with Bs mixing.