Nuclear Moments Violating Fundamental Symmetries: Testing Unification Theories and Searching for Dark Matter

Measurements of nuclear moments that violate parity (P) and time-reversal invariance (T) provide critical tests of unification theories predicting CP violation and the matter–antimatter asymmetry observed in the Universe (baryogenesis). These T,P-violating moments include the electric dipole moment (EDM), Schiff moment, magnetic quadrupole moment, and octupole moment. T,P-violating nuclear moments are primarily generated by T,P-violating nuclear forces, with smaller contributions arising from the proton and neutron EDMs.

Oscillating T,P-violating nuclear moments can be induced through interactions with oscillating axion dark matter fields, making their measurement a promising method for dark matter detection. These moments exhibit collective enhancement in deformed nuclei. For example, the Schiff moment is enhanced by factors of 100–1000 in nuclei with octupole deformation, while the magnetic quadrupole moment is significantly enhanced in quadrupole-deformed nuclei.

The interaction of electrons with T,P-violating nuclear moments results in atomic and molecular EDMs, which are directly measurable. Nuclear EDMs are entirely screened in neutral systems, meaning atomic and molecular EDMs originate from interactions of electrons with nuclear Schiff and magnetic quadrupole moments. However, nuclear EDM screening can be circumvented in ions, non-stationary states, and experiments using oscillating electric fields.

Additionally, the nuclear anapole moment (a parity-violating magnetic moment) has been experimentally observed in ¹³³Cs. Ongoing experiments aim to measure the anapole moments of other nuclei, further advancing our understanding of fundamental symmetries and their violations.