Signatures of an extra Z0 gauge boson in elastic e--proton scattering

We consider popular extensions of the standard model which include new heavy Z0 gauge bosons, and examine their effect on parity violation in elastic electron-proton scattering at intermediate energies. These extensions all involve an effective low-energy symmetry group SU(3)/sub C/xSU(2)/sub L/ xU(1)/sub Y/x(U)1/sub Y//sub '/. In several special cases motivated by grand unified theories based on SO(10) and E6, we find that a parity measurement with an accuracy of a few percent would raise the existing mass bounds on a heavy Z0, and would reduce the range of allowed mixing angles by as much as a factor of 5. In some cases, the lower bound on a heavy Z0 mass would be raised by more than 100 GeV over current limits