Electric dipole moment of theWboson and the radiation amplitude zero

The effect of an electric dipole moment (EDM) of the W boson is studied in the radiative decay $W^{\mathrm{-}}$→ūdγ. It is shown that the radiation amplitude zero which is present in this process provides a sensitive test of the possible compositeness of the W. The two possibilities, a large EDM (λ≥1) and a significant magnetic moment (κ≠1) can in principle be distinguished.