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We explore the possibility that lepton family numbers and baryon number aresuch good symmetries of Nature because they are the global remnant of aspontaneously broken gauge symmetry. An almost arbitrary linear combination ofthese symmetries (together with a component of global hypercharge) can beconsistently gauged, if the Standard Model (SM) fermion content is augmented bythree chiral SM singlet states. Within this framework of $U(1)$ extensions ofthe SM one generically expects flavour non-universality to emerge in thecharged leptons, in such a way that naturally prevents lepton flavourviolation, by aligning the mass and weak eigenbases. For quarks, all the SMYukawa couplings responsible for their observed masses and mixings arise at therenormalisable level. We perform fits to show that models in this class canexplain $R_{K^{(\ast)}}$ and the other neutral current $B$ anomaly data if weintroduce a heavy vector-like quark to mediate the required quark flavourviolation, while simultaneously satisfying other constraints from direct$Z^\prime$ searches at the LHC, $B_s$ meson mixing, a number of electroweakprecision observables, and neutrino trident production. Within thissymmetry-motivated framework of models, we find interesting implications forthe flavour anomalies; notably, any axial couplings of the $Z^\prime$ toelectrons and muons must be flavour universal, with the flavour universalityviolation arising solely from the vector-like couplings. We also comment on thegeneration of neutrino masses in these models.

Gauging the accidental symmetries of the Standard Model, and implications for the flavour anomalies