Some advantages of SUSY SU(4)xSU(2)LxSU(2)R model in string inspired SO(10) GUT's

A D-parity violated SUSY SU(4) x SU(I)(L) x SU(2)(R) gauge model with the Higgs sector 2{(4, 1, 2) + ((4) over bar, 1, 2)} + (1, 2, 2) + some (I, I, 1)'s is shown to have the following advantages: (i) It is a very simple solution that satisfies M-X = M-string approximate to 0.5 x 10(18) GeV and M-INT approximate to 5 x 10(11) GeV in superstring inspired SO(10) GUT's. (ii) The proton is stable by the automatic "doublet-triplet splitting" closely connected with the D-parity violation. (iii) The minimization of SUSY one-loop effective potential in a toy model suggests that the SO(10) gauge theory tends to break dynamically down to the SU(4) x SU(2)(L) x SU(2)(R) model.