  Flavor changing neutral current $|\Delta B|=|\Delta S|=1$ processes are
sensitive to possible new physics at the electroweak scale and beyond,
providing detailed information about flavor, chirality and Lorentz structure.
Recently the LHCb collaboration announced a $2.6 \sigma$ deviation in the
measurement of $R_K={\cal{B}}(\bar B \to \bar K \mu \mu)/{\cal{B}}(\bar B \to
\bar K ee)$ from the standard model's prediction of lepton universality. We
identify dimension six operators which could explain this deviation and study
constraints from other measurements. Vector and axial-vector four-fermion
operators with flavor structure $\bar s b \bar \ell \ell$ can provide a good
description of the data. Tensor operators cannot describe the data.
Pseudo-scalar and scalar operators only fit the data with some fine-tuning;
they can be further probed with the $\bar B \to \bar K ee$ angular
distribution. The data appears to point towards $C_9^{\rm NP \mu} =
-C_{10}^{\rm NP \mu }<0$, an $SU(2)_{L}$ invariant direction in parameter space
supported by $R_K$, the $\bar B \to \bar K^* \mu \mu$ forward-backward
asymmetry and the $\bar B_s \to \mu \mu$ branching ratio, which is currently
allowed to be smaller than the standard model prediction. We present two
leptoquark models which can explain the FCNC data and give predictions for the
LHC and rare decays.
