New physics in b → sμ+ μ- after the measurement of RK

The recent measurement of R-K* is yet another hint of new physics (NP) and supports the idea that it is present in b -> s mu(+) mu(-) decays. We perform a combined model-independent and model-dependent analysis in order to deduce properties of this NP. Like others, we find that the NP must obey one of two scenarios: (I) C-9(mu mu) (NP) < 0 or (II) C-9(mu mu) (NP) = -C-10(mu mu) (NP) < 0. A third scenario, (III) C-9(mu mu) (NP) = -C-9(mu mu) (NP), is rejected largely because it predicts R-K = 1, in disagreement with experiment. The simplest NP models involve the tree-level exchange of a leptoquark (LQ) or a Z' boson. We show that scenario II can arise in LQ or Z' models, but scenario I is only possible with a Z'. Fits to Z' models must take into account the additional constraints from B-s(0)-(B) over bar (0)(s) mixing and neutrino trident production. Although the LQs must be heavy, O( TeV), we find that the Z' can be light, e.g., M-Z' = 10 GeV or 200 MeV.