A simple SU(5) model with unification near the Planck scale
  We study unification in the SU(5) model with an extra Dirac multiplet in the ${\bf 24}$ representation. After spontaneous symmetry breaking we have at low energies a singlet, a colorless triplet and a neutral color-octet. All other particles can be taken at the unification scale. This combination leads to a unification very near the Planck scale. The triplet is light, its neutral component is a dark matter candidate. The model is in agreement with a recently derived anomaly condition, that implies that the number of (Weyl)-fermions has to be a multiple of 16. 
J. J. van der Bij
hep-ph hep-th