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The CP phase in the strong sector comes from a topological term (a total derivative) $$\require{cancel} \mathcal L_{\cancel{CP}} \propto \theta_\mathrm{QCD} \epsilon^{\mu \nu \rho \sigma} G_{\mu \nu} G_{\rho \sigma},$$ where $G_{\mu \nu}$ is the gluon field-strength. Such an operator can never be produced as an effective operator from weak interactions, ...