RK and RK* beyond the standard model
AbstractMeasurements of the ratio of B→K*μμ to B→K*ee branching fractions, RK*, by the LHCb Collaboration strengthen the hints from previous studies with pseudoscalar kaons, RK, for the breakdown of lepton universality, and therefore the Standard Model (SM), to ∼3.5σ. Complementarity between RK and RK* allows us to pin down the Dirac structure of the new contributions to be predominantly SM-like chiral, with possible admixture of chirality-flipped contributions of up to O(few10%). Scalar and vector leptoquark representations (S3,V1,V3) plus possible (S˜2,V2) admixture can explain RK,K* via tree-level exchange. Flavor models naturally predict leptoquark masses not exceeding a few TeV, with couplings to third-generation quarks at O(0.1), implying that this scenario can be directly tested at the LHC.