TWISTED N = 2 SUPERCONFORMAL MODELS AND LEFT-RIGHT ASYMMETRIC STRING COMPACTIFICATIONS

We consider string compactifications obtained by modding tensor products of N = 2 superconformal models by discrete symmetries. The presence of discrete torsion modifies the usual generalized GSO projection and gives rise to (2,2), (0,2) or non-supersymmetric compactifications depending on its (quantized) value. We construct left-right asymmetric compactifications by twisting differently left- and right-movers of the N = 2 blocks. Some of these constructions provide a generalization of the concept of asymmetric orbifolds to non-toroidal (Calabi-Yau) varieties. We prove that all these models can be interpreted as left-right symmetric compactifications in the presence of discrete torsion. This suggests that all presently known four-dimensional strings may be equivalently understood as compactifications of the 10-dimensional Heterotic string in the presence of background fields.