Discrete Gauge Anomalies in Orbifold Models

Discrete gauge anomalies in string theory models are discussed. Results of a study of ~ 10,000 orbifold compactifications of the heterotic string and ~30 Type II models are reported. The study finds that in all models examined, the discrete gauge anomalies can be cancelled through a Green-Schwarz type mechanism. The work begins with a discussion of discrete gauge symmetries. There is an introduction to string theory, a chapter on compactification, and an explanation of orbifold models. The results of the computer search of orbifold compactifications of heterotic string models is then discussed. In Part II, there are introductory chapters explaining conformal field theory and superconformal field theory. Type II string models with gauge symmetries are then described, and the results of an examination of discrete gauge anomalies in these models is reported. A final chapter discusses the overall results and questions for future research. There are five appendices describing important topics used throughout the thesis.