Lepton Flavor Non-Universality in B-meson Decays from a U(2) Flavor Model

Understand

We address the recent anomalies in semi-leptonic $B$-meson decays using a model of fermion masses based on the $U(2)$ flavor symmetry.

• The new contributions to $b \to s \ell \ell$ transitions arise due to a tree-level exchange of a $Z^\prime$ vector boson gauging a $U(1)$ subgroup of the flavor symmetry.
• They are controlled by a single parameter and are approximately aligned to the Standard Model prediction, with constructive interference in the $e$-channel and destructive interference in the $\mu$-channel.
• The current experimental data on semi-leptonic $B$-meson decays can be very well reproduced without violating existing constraints from flavor violation in the quark and lepton sectors.