We give a formula to determine the intermediate mass scale of SU(N) grand unification with a nontrivial charge assignment. Using the limit on the proton lifetime and the cosmological requirement on the intermediate mass scale, its application to SU(9) determines the symmetry-breaking pattern and the nontrivial charge assignment.

• Received 26 December 1984

DOI:https://doi.org/10.1103/PhysRevD.31.2964