Simultaneous Explanation of the $R_K$ and $R(D^{(*)})$ Puzzles

Understand

At present, there are several hints of lepton flavor non-universality.

• The LHCb Collaboration has measured $R_K\equiv{\cal B}(B^+ \to K^+ \mu^+ \mu^-)/{\cal B}(B^+ \to K^+ e^+ e^-)$, and the BaBar Collaboration has measured $R(D^{(*)}) \equiv {\cal B}({\bar B} \to D^{(*)+} \tau^- {\bar\nu}_\tau) / {\cal B}({\bar B} \to D^{(*)+} \ell^- {\bar\nu}_\ell)$ ($\ell = e,\mu$).
• In all cases, the experimental results differ from the standard model predictions by 2-3$\sigma$.
• Recently, an explanation of the $R_K$ puzzle was proposed in which new physics (NP) generates a neutral-current operator involving only third-generation particles.