The amplitudes Z’→Zγ and Z’→ZZ in models with an additional U’(1) gauge group beyond the standard SU(2)×U(1) electroweak theory are induced via fermion loops of ordinary states u, d, e, ν, etc., and heavy exotic states which will not cancel among themselves though the anomaly condition is satisfied. An ${\mathrm{E}}_6$ model is used as an example for the illustration. The new heavy neutral gauge boson Z’ could decay into Zγ and ZZ with branching ratios Γ(Z’→Zγ)/ Γ(Z’→$e^{+}$$e^{\mathrm{-}}$)∼${10}^{\mathrm{-}6}$ and Γ(Z’→ZZ)/Γ(Z’→${\mathrm{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$)∼${10}^{\mathrm{-}5}$.

• Received 23 October 1987

DOI:https://doi.org/10.1103/PhysRevD.38.850