An Explicit Way to Break CP Symmetry in the Standard Model.

We study how CP symmetry can be broken in the standard model of electroweak interactions from the theoretical end. Through the analysis of origin of a complex phase in CKM matrix, two necessary but not sufficient conditions are revealed. Inspecting with these conditions, we find CP violating phase appear in several interesting circumstances with $S_N$ symmetries among quark generations. Though the CP strength thus derived is orders stronger than the one detected in present high energy experiments. If we consider no such $S_N$-symmetries are detected in our present universe and they should exist only in very early stages of our universe when temperature was extremely high. Surely the CP strength changes as the temperature dropped and symmetries were broken. Besides, this hypothesis can even account for at least four in the ten orders discrepancy between the cosmologically observed Baryon Asymmetry in the Universe (BAU) and that detected in high energy physics. This gives us a new and interesting aspect to realize the ignition of CP violation.