Reanalysis of strongCP-violating effects in chiral perturbation theory

Strong $\mathrm{CP}$-violating effects induced by the QCD $\theta$ term, e.g., the $\eta \to \pi \pi$ decay, the $\mathrm{CP}$-odd pion-nucleon coupling, and the electric dipole moment of the neutron are reanalyzed in chiral perturbation theory in which strong $\mathrm{CP}$ violation manifests itself in the meson and baryon sectors. Corrections to previous current-algebra results are calculated. We show that strong $\mathrm{CP}$ phenomena do respect the general constraint that, as stressed recently by Aoki and Hatsuda, they vanish in the absence of the gluonic anomaly and/or in the chiral limit. The neutron electric dipole moment induced at the tree level is reevaluated and found to be constructive in sign and comparable in magnitude with the leading nonanalytic contribution due to one-loop diagrams.