Extra fermions in E6 superstring theories

In E6 superstring theories, there are new fermion fields which lie in the 27-dimensional representation along with the known fermions. We examine possible production modes of these exotic fermions and their likely decays. Whereas e+e- collider data exclude new charged fermions with masses below 23 GeV, it appears that present pp-bar collider data for dimuons and for isolated single electrons exclude exotic quarks with masses below 30 GeV and considerable regions of lepton mass assignments in the range 20-45 GeV (assuming m/sub E/>mE,m/sub N//sub E/). We place constraints on the mixings of the exotic fermions from experimental limits on flavor-changing neutral currents and the observed weak universality of charged-current interactions. The decays of the exotic h quark (singlet, charge -(1/3)) satisfy the bound GAMMA(h→de+e-)/GAMMA(h→ueν)> or approx. =12%. Production and decays of very heavy exotics are also considered