Extra gauge bosons inE6

Recent developments in superstring theories have renewed interest in ${\mathrm{E}}_6$ as the group for grand unification. ${\mathrm{E}}_6$ has rank 6, two more than the standard model, so that an ${\mathrm{E}}_6$ grand unified theory can have extra gauge bosons. For example, it can have extra low-energy Z’s. If there is just one extra Z at low energy, it can be a mixture of the two extra U(1)’s present in ${\mathrm{E}}_6$. We parametrize this mixing by an angle theta. We consider the effects of Z(theta) in neutral currents, putting limits on its mass. In addition, we consider the branching ratios, Drell-Yan production, and forward-backward asymmetries for Z(theta). Another possibility is that, in addition to one extra Z, there is an extra SU(2) present in the low-energy theory. It is SU(2${)}_{\mathrm{I}}$, the SU(2) which commutes with the electromagnetic charge. We consider the effects of the $W_I$, which are electromagnetically neutral, in production of exotic particles and other rare processes, particularly flavor-changing neutral currents.