Field momentum and the reality of the Dirac String

Abstract: It is well known that a magnetic monopole-electric charge system carries an angular momentum in its electromagnetic fields. Here we show that in the Dirac string formulation of magnetic charge the monopole-electric charge system also carries a momentum in its electromagnetic fields. This overlooked field momentum arises from the Coulomb electric field of the electric charge and the solenoidal magnetic field of the Dirac string. This implies that the monopole-charge system must either: (i) carry a ``hidden momentum" in the string, indicating that the string is real, or (ii) that the monopole-charge system violates the center-of-energy theorem. The overall conclusion is that the Dirac monopole with a {\it regulated} Dirac string is not a true monopole, and is not even a good effective description for topological monopoles ({\it e.g.} the 't Hooft-Polyakov monopole outside the core).