Implications ofE6grand unification

We study the allowed intermediate symmetries and the charged- and neutral-fermion masses in ${\mathrm{E}}_6$ grand-unification theories. We isolate an interesting symmetry-breaking chain where a neutral lepton with mass in the GeV range exists. Such a lepton will contribute to the width of the Z boson, which is an interesting feature of the ${\mathrm{E}}_6$ model.