Anomalies in 8Be nuclear transitions and (g-2)e,μ: towards a minimal combined explanation

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 Be-8 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 Be-8 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,mu) 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 Be-8 particularly predictive. The underlying idea of this minimal prototype model can be readily incorporated into other protophobic U(1) extensions of the Standard Model.