Motivated by a simultaneous explanation of the apparent discrepancies in the light charged lepton anomalous magnetic dipole moments, and the anomalous internal pair creation in 8 Be nuclear transitions, we explore a simple New Physics model, based on an extension of the Standard Model gauge group by a U(1) B−L. The model further includes heavy vector-like fermion fields, as well as an extra scalar responsible for the low-scale breaking of U(1) B−L , which gives rise to a light Z boson. The new fields and currents allow to explain the anomalous internal pair creation in 8 Be while being consistent with various experimental constraints. Interestingly, we find that the contributions of the Z and the new U(1) B−L-breaking scalar can also successfully account for both (g−2) e,µ anomalies; the strong phenomenological constraints on the model's parameter space ultimately render the combined explanation of (g − 2) e and the anomalous internal pair creation in 8 Be particularly predictive. The underlying idea of this minimal "prototype model" can be readily incorporated into other protophobic U(1) extensions of the Standard Model.

In order to simultaneously account for both R D ( * ) and R K ( * ) anomalies in B-decays, we consider an extension of the Standard Model by a single vector leptoquark field, and study how one can achieve the required lepton flavour non-universality, starting from a priori universal gauge couplings. While the unitary quark-lepton mixing induced by SU (2) L breaking is insufficient, we find that effectively nonunitary mixings hold the key to simultaneously address the R K ( * ) and R D ( * ) anomalies. As an intermediate step towards various UV-complete models, we show that the mixings of charged leptons with additional vector-like heavy leptons successfully provide a nonunitary framework to explain R K ( * ) and R D ( * ) . These realisations have a strong impact for electroweak precision observables and for flavour violating ones: isosinglet heavy lepton realisations are already excluded due to excessive contributions to lepton flavour violating Z-decays. Furthermore, in the near future, the expected progress in the sensitivity of charged lepton flavour violation experiments should allow to fully probe this class of vector leptoquark models.