DO-TH 17/04 RK and RK∗ beyond the Standard Model

RK and RK∗ beyond the Standard Model Gudrun Hiller ∗ and Ivan Nǐsandžić † Institut für Physik, Technische Universität Dortmund, D-44221 Dortmund, Germany Measurements 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 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 (S̃2, 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.