Nuclear structure and the search for collective enhancement of P,T -violating Schiff moments

The search for the manifestations of new physics beyond the standard model in atomic and nuclear phenomena is pursued by several experimental groups. The discovery of the atomic electric dipole moment (EDM) would reveal the simultaneous violation of parity and time-reversal invariance. The EDM can be induced by -odd forces between the nucleus and atomic electrons. As the nuclear dipole moment is screened according to the Schiff theorem, the appropriate nuclear operator is the Schiff moment that may exist in nuclei under -violation. We briefly review the current experimental situation and discuss more in detail the ideas concerning possible collective mechanisms for the enhancement of the nuclear Schiff moment. The most promising directions are related to the coexistence of octupole and quadrupole collective modes, either in the form of static deformation or as soft vibrational excitations. The search for enhancement is important for widening the pool of nuclei as candidates for the atomic EDM as well as for development of nuclear many-body theory beyond standard mean-field and random phase approximations.