Non-abelian gauge extensions for B-decay anomalies

Abstract

We study the generic features of minimal gauge extensions of the Standard Model in view of recent hints of lepton-flavor non-universality in semi-leptonic $b\to s{\ell }^{+}{\ell }^{-}$ and $b\to c\ell \nu$ decays. We classify the possible models according to the symmetry-breaking pattern and the source of flavor non-universality. We find that in viable models the ${\mathrm{SU}(2)}_L$ factor is embedded non-trivially in the extended gauge group, and that gauge couplings should be universal, hinting to the presence of new degrees of freedom sourcing non-universality. Finally, we provide an explicit model that can explain the $B$-decay anomalies in a coherent way and confront it with the relevant phenomenological constraints.

Comments: 8 pages, 2 figures; discussion improved, a figure and references added; conclusions unchanged