The magnetic moment of W and the scale of composite weak bosons

If the W boson is composite, its magnetic moment deviates from the value of the standard electroweak gauge theory. We derive some quantitative relations between this deviation and the scale of compositeness from partial-wave unitarity at high energies and from the anomalous magnetic moment of the muon. If the W magnetic moment differs from the standard value by one unit of {e}/{2m _W}, for instance, the compositeness scale must be lower than about 1 TeV. An improvement in accuracy of the measurement of the magnetic moment of the muon by another order of magnitude may lead us to a valuable insight into the compositeness scale of the W boson.