CLASSIFICATION OF FLAT DIRECTIONS IN PERTURBATIVE HETEROTIC SUPERSTRING VACUA WITH ANOMALOUS U(1)

We develop techniques to classify D- and F-flat directions for N = 1 s upersymmetric string vacua of the perturbative heterotic string theory , which possess an anomalous U(1) gauge group at the tree level. Genus -one corrections generate a Fayet-Iliopoulos term for the D-term of U( 1)A, which is cancelled by non-zero vacuum expectation values (VEVs) o f certain massless multiplets, in such a way that the anomalous U(1) i s broken, while maintaining the D- and F-flatness of the effective fie ld theory. A systematic analysis of flat directions is given for non-z ero VEVs of non-Abelian singlets, and the techniques are illustrated f or a specific model. The approach sets the stage to classify the D- an d F-flat directions for a large class of perturbative string vacua. Th is classification is a prerequisite to systematically addressing the p henomenological consequences of these models. (C) 1998 Elsevier Scienc e B.V.