Electroweak theories based on gauge groups $\mathrm{SU}{\mathrm{}\left(2\right)\mathrm{}}_L\times \mathrm{U}\mathrm{}\left(1\right)\mathrm{}\times \mathrm{U}\mathrm{}\left(1\right)\mathrm{}\times \mathrm{U}\mathrm{}\left(1\right)\mathrm{}$ arising from the spontaneous breakdown of ${\mathrm{E}}_6$ are examined. The neutral-current interactions at low $Q^2$ in two such three-$Z$ models are derived. One neutral boson with a mass a few percent lighter than the standard-model $Z^0$ mass and two additional $Z\text{'}\mathrm{s}$ as light as 300 GeV-1 TeV are allowed.

• Received 5 April 1982

DOI:https://doi.org/10.1103/PhysRevD.26.2388