The LHCb Collaboration’s measurement of $R_K=\mathcal{B}(B^{+}\to K^{+}{\mu }^{+}{\mu }^{-})/\mathcal{B}(B^{+}\to K^{+}{e}^{+}{e}^{-})$ lies $2.6\sigma$ below the Standard Model prediction. Several groups suggest this deficit to result from new lepton nonuniversal interactions of muons. But nonuniversal leptonic interactions imply lepton flavor violation in $B$ decays at rates much larger than are expected in the Standard Model. A simple model shows that these rates could lie just below current limits. An interesting consequence of our model, that $\mathcal{B}(B_s\to {\mu }^{+}{\mu }^{-}{)}_{\text{exp}}/\mathcal{B}(B_s\to {\mu }^{+}{\mu }^{-}{)}_{\mathrm{SM}}\cong R_K\cong 0.75$, is compatible with recent measurements of these rates. We stress the importance of searches for lepton flavor violations, especially for $B\to K\mu e$, $K\mu \tau$, and $B_s\to \mu e$, $\mu \tau$.

• Received 15 November 2014

DOI:https://doi.org/10.1103/PhysRevLett.114.091801