On the mixing and production of exotic fermions inE6

The mixings between exotic fermions in ${\mathrm{E}}_6$ 27-plets (a Q=-(1/3) isosinglet quark h and charged and neutral leptons E and ${\nu }_E$) and their familiar counterparts d, e, and ${\nu }_e$ are discussed and constraints from electroweak neutral-current data on such mixings are examined. We find off-diagonal couplings dh¯$Z^0$, eĒ$Z^0$, and ${\nu }_e$ν${¯}_E$ $Z^0$ and propose new methods for single production of such new fermions in $e^{+}$ $e^{\mathrm{-}}$ collisions and Z decay. Such couplings also lead (in general) to flavor-changing neutral currents and we examine constraints on the masses and mixings of the h quarks which can be derived from the $K^0$-K${¯}^0$ system and $K_L$→${\mu }^{+}$ ${\mu }^{\mathrm{-}}$.