MEASURE OF STRONG CP VIOLATION

We investigate a controversial issue on the measure of CP violation in strong interactions. In the presence of nontrivial topological gauge configurations, the theta term in QCD has a profound effect: it breaks the CP symmetry. The CP-violating amplitude is shown to be determined by the vacuum tunneling process, where the semiclassical method makes most sense. We discuss a long-standing dispute on whether or not the instanton dynamics satisfies the anomalous Ward identity (AWI). The strong CP-violation measure, when complying with the vacuum alignment, is proportional to the topological susceptibility. To solve the IR divergence problem of the instanton computation, we present a ''classically gauged'' Georgi-Manohar model and derive an effective potential which uniquely determines an explicit U(1)A symmetry breaking sector. The CP-violation effects are analyzed in this model. It is shown that the strong CP problem and the U(1) problem are closely related. Some possible solutions to both problems axe also discussed with new insights.