Symmetry and Superstring Phenomenology

Calabi-Yau compactifications of the heterotic string, and their orbifold limits, can reproduce the gauge symmetries and particle spectrum of the Standard Model and its minimal supersymmetric extension (MSSM). They also include a. "hidden" gauge sector that can induce supersymmetry breaking, as required by observation. The "moduli" (gauge singlet) sector of the theory has additional symmetries that can lead to further desirable properties in the low energy theory. This is illustrated by the example of a possible relation between the discrete SL(2, Z) symmetry from string theory called "T-duality" and the discrete symmetry "R-parity" of the MSSM, which is needed for consistency with observation.