(0,2) LANDAU-GINZBURG THEORY

A large class of (0,2) Calabi-Yau sigma-models and Landau-Ginzburg orbifolds are shown to arise as different ''phases'' of supersymmetric gauge theories. We find a phenomenon in the Landau-Ginzburg phase which may enable one to understand which Calabi-Yau sigma-models evade destabilization by worldsheet instantons. Examples of (0,2) Landau-Ginzburg vacua are analyzed in detail, and several novel features of (0,2) models are discussed. In particular, we find that (0,2) models can have different quantum symmetries from the (2,2) models built on the same Calabi-Yau manifold, and that a new kind of topology change can occur in (0,2) models of string theory.