Neutron Electric Dipole Moment - Theory

Theory

A permanent electric dipole moment of a fundamental particle violates both parity (P) and time reversal symmetry (T). This can be understood by examining the neutron with its magnetic dipole moment and hypothetical electric dipole moment. Under time reversal, the magnetic dipole moment changes its direction, whereas the electric dipole moment stays unchanged. Under parity, the electric dipole moment changes its direction but not the magnetic dipole moment. As the resulting system under P and T is not symmetric with respect to the initial system, these symmetries are violated in the case of the existence of an EDM. Having also CPT symmetry, the combined symmetry CP is violated as well.