The leading T-conserving P-nonconserving (PNC) electromagnetic coupling to the nucleon or nucleus is known as the anapole moment. We evaluate the pion-cloud contribution to the nucleon anapole moment, and the enhancements in nuclei associated with meson-exchange currents and with the mixing of the nuclear ground state with opposite-parity excited states. We find that the anapole moment becomes the dominant PNC spin-dependent coupling in heavy nuclei.

• Received 1 May 1989

DOI:https://doi.org/10.1103/PhysRevLett.63.949