Cp Symmetry and Fermion Masses in O(10) Grand Unification Models

O(10) grand unification models which do not necessarily have an extra global symmetry are discussed, taking the model with one 10-plet in the Yukawa sector as an example. A strong correlation between mass ratios and CP is found. The mass relation mt/mb=vu/vd is recovered when GW=0; and another special relation mt/mb=GE/GW appears when vd=0, where GE,W are Yukawa coupling constants and vu,d are vevs. To facilitate this discussion, a set of O(10) γ-matrices is offered based on a physical representation of the spinors and that of the vector of the SO(10) group. Flavor changing neutral currents in such models are also discussed.