Interpreting Hints for Lepton Flavor Universality Violation

Abstract

We interpret the recent hints for lepton flavor universality violation in rare $B$ meson decays. Based on a model-independent effective Hamiltonian approach, we determine regions of new physics parameter space that give a good description of the experimental data on $R_K$ and $R_{K^*}$, which is in tension with Standard Model predictions. We suggest further measurements that can help narrowing down viable new physics explanations. We stress that the measured values of $R_K$ and $R_{K^*}$ are fully compatible with new physics explanations of other anomalies in rare $B$ meson decays based on the $b \to s \mu\mu$ transition. If the hints for lepton flavor universality violation are first signs of new physics, perturbative unitarity implies new phenomena below a scale of $\sim 100$ TeV.