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 → sℓℓ transitions arise due to a tree-level exchange of a Z′ 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 μ-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 → sℓℓ transitions and also by future electroweak precision tests, direct Z′ searches, and μ-e conversion in nuclei.