The $Z_2\times Z_2$ Orbifold and the SUSY Flavor Problem
  The characteristic property of the $Z_2\times Z_2$ orbifold is its cyclic permutation symmetry. It is argued that this property may be instrumental in explaining simultaneously the fermion mass hierarchy and the squark mass degeneracy. Detailed studies in free fermionic models that preserve the cyclic permutation symmetry of anomalous U(1) charges of the three generations are discussed. 
Alon E. Faraggi