HIGHER TWISTED SECTOR COUPLINGS OF Z(N) ORBIFOLDS

We derive the basic correlation functions of twist fields coming from arbitrary twisted sectors in symmetric Z(N) orbifold conformal field t heories, keeping all the admissible marginal perturbations, in particu lar those corresponding to the antisymmetric-tensor background field. This allows a thorough investigation of modular symmetries in this typ e of string compactification. Such a study is explicitly carried out f or the group generated by duality transformations. Thus, apart from be ing of phenomenological use, our couplings are also interesting from t he mathematical point of view as they represent automorphic functions for a large class of discrete groups.