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

Abstract

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 $\hat{I}¼$-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. Our model will be tested by new measurements of $b\to s\ell \ell$ transitions and also by future electroweak precision tests, direct $Z^{\prime }$ searches, and $\hat{I}¼$-$e$ conversion in nuclei.

23 pages, 2 figures, references added, matches published version