INTERMEDIATE SCALES, MU-PARAMETER, AND FERMION MASSES FROM STRING MODELS

We address intermediate scales within a class of string models. The in termediate scales occur due to the SM singlets Si acquiring non-zero V EVs due to radiative breaking; the mass squared m(i)(2) of S-i is driv en negative at mu(rad) due to Omicron(1) Yukawa couplings of S-i to ex otic particles (calculable in a class of string models). The actual VE V of S-i depends on the relative magnitude of the non-renormalizable t erms of the type (S) over cap(i)(K+3)/M-K in the superpotential. We ma inly consider the case in which the S-i are charged under an additiona l non-anomalous U(1)' gauge symmetry and the VEVs occur along F-and D- flat directions. We explore various scenarios in detail, depending on the type of Yukawa couplings to the exotic particles and on the initia l boundary values of the soft SUSY breaking parameters. We then addres s the implications of these scenarios for the mu parameter and the fer mionic masses of the standard model.