How Large is the "Natural" Magnetic Moment?

Abstract

The "natural" magntic moment of a particle of spin S is generally assumed to be that given by the Belinfante conjecture and has the value g=1/S for its gyromagnetic ratio. Thus, for the spin 1/2 electron we find the Dirac value $g_e=2$. However, in the standard model the charged W boson, a spin one particle, is found to have the value $g_{W^+}=2$. We show how this result comes about and argue that the "natural" value for any particle of spin S should be g=2, independent of spin.