Hierarchical Supersymmetry Breaking in Superstring Derived   Standard--like Models
  We examine the problem of supersymmetry breaking in realistic superstring standard--like models which are constructed in the free fermionic formulation. We impose a supersymmetric vacuum at the Planck scale by requiring vanishing F and D constraints at the cubic level of the superpotential. We then study possible scenarios for supersymmetry breaking by examining the role of nonrenormalizable terms and hidden sector gaugino and matter condensates. We argue that in some scenarios hierarchical supersymmetry breaking in the observable sector is possible. 
Alon E. Faraggi and Edi Halyo