Matter parity, intermediate scale breaking, andsin2θWin Calabi-Yau superstring models

Consequences of matter-parity invariance on intermediate scale breaking in three-generation Calabi-Yau superstring models are discussed. It is shown that values of ${\sin }^2$ ${\mathrm{\theta }}_{\mathrm{W}}$ in conformity with the current experimental limits can arise in the Calabi-Yau models when the extra families and mirror families gain superheavy masses through nonrenormalizable interactions. A small number of exotic leptons with electroweak-scale masses remain and may be accessible at accelerator energies.