Product Groups, Discrete Symmetries, and Grand Unification
  We present GUT models based on an $SU(5)\times SU(5)$ GUT group. These models maintain the main successes of simple-group GUTs but permit simple solutions to the doublet-triplet splitting problem. Moreover, GUT breaking is triggered by supersymmetry breaking so that the GUT scale is naturally generated as a combination of the Planck scale and the supersymmetry breaking scale. 
Yael Shadmi