A possible solution of the doublet-triplet splitting problem in extended SU(N ≥ 8) SUSY GUTs

Abstract A generalization of the “custodial symmetry” mechanism which leads to a natural (without fine tuning) explanation of the doublet-triplet hierarchy is suggested in the frame of extended SU( N ≥ 8) SUSY GUTs. It is shown also that such type of SUSY GUT can predict the value of the strong gauge coupling constant α s ( M Z ) consistent with present experimental data.