Electric-dipole moments of elementary particles

Elementary particles can have electric-dipole moments only if there is a failure of symmetry under both parity (P) and time-reversal (T) transformations. It is now known experimentally that there are in nature failures of both of these symmetries, but so far the only experimental manifestations of failures of T symmetry have been limited to the neutral kaon system. Most theories that are consistent with the observed T-violating decay of K L 0 also predict non-zero values for the electric-dipole moments of elementary particles, with many of the predicted values being within the range of experimental verification. However, so far no electric-dipole moment has been observed for any elementary particle. Experiments setting limits on the electric-dipole moment, eD, of elementary particles are reviewed. The most sensitive tests of theory are with the neutron, for which D