Electric Dipole Moment of a Nucleon

A violation of time-reversal invariance of any of the elementary particle interactions would imply the existence of a static electric-dipole moment for all these particles. We make here a theoretical estimate of the electric-dipole moment (μₑ) of a bare nucleon, assuming the existence of an intermediate vector boson (W) and a small violation of T invariance for the weak interactions. With the existing experimental upper limit for T violation from polarized neutron decay, we find that μₑemN×10^-7. Since a value for μₑ somewhat smaller than this upper limit seems to be experimentally observable, such an experiment would provide a good test for T invariance as well as for the existence of W mesons.