A renormalizable supersymmetric SO(10) model with natural   doublet-triplet splitting
  We propose a renormalizable supersymmetric SO(10) model where the doublet-triplet splitting problem is solved using the Dimopoulos-Wilczek mechanism. An unwanted coupling is forbidden through a filter sector. To suppress proton decay without spoiling gauge coupling unification, there is a problem in the weak doublets which requires further improvements. 
Ying-Kang Chen and Da-Xin Zhang
hep-ph