Atomki Anomaly in Family-Dependent U (1)′ Extension of the Standard Model

In the context of a gauge invariant, nonanomalous, and family-dependent (nonuniversal) U(1)′ extension of the Standard Model, wherein a new high-scale mechanism generates masses and couplings for the first two fermion generations and the standard Higgs mechanism does so for the third one, we find solutions to the anomaly observed by the Atomki Collaboration in the decay of excited states of beryllium, in the form of a very light Z′ state, stemming from the U(1)′ symmetry breaking, with significant axial couplings so as to evade a variety of low-scale experimental constraints.