Phenomenological Implications of the Blown-up Orbifolds*+

We discuss the structure of the effective Lagrangian for the (2,2) ZN orbifolds and the corresponding Calabi-Yau manifolds which are obtained by “blowing-up” the orbifold singularities. The method to “blow-up” such singularities is reviewed.’ Results are exact at the string tree-level. In particular the question of generating an intermediate scale MI in such models is addressed. It is shown that for ZN orbifolds (except one) and the corresponding blown-up orbifolds which are compactified on any six-torus T6 which can be obtained by continuously deforming -T4 @T2, all the terms of the type (27mK are absent from the effective superpotential, thus questioning the mechanism for generating a large intermediate scale for such compactifications. Lnvited *talk presented at the Eight Workshop on Grand Unifications, Syracuse, New York, April 16-18, 1987 *Work supported in by the Department of Energy, contracts DE-AC03-76SF00515