Towards the Non-Chiral Extension of SM and MSSM
  We show that in some SU(N) type GUTs with the complementary pairs of the conjugated fermion multiplets there naturally appear the relatively light ($M\ll M_{GUT}$) vectorlike fermions which considerably modify the desert physics. In the non-SUSY case they can provide for the unification of the standard coupling constant $\alpha_1$, $\alpha_2$ and $\alpha_S$ whereas in the SUSY case they can increase the unification point up to the string unification limit and decrease $\alpha_S(M_Z)$ down to the value predicted from the low energy physics. 
J.L.Chkareuli, I.G.Gogoladze and A.B.Kobakhidze