Nonlinear gravitational effects and magnetic monopoles

The Einstein-Maxwell equations for systems of particles possessing electric and magnetic charge are considered. The consequences of the linear and nonlinear theories are contrasted, by considering a known class of exact solutions. In particular, for these systems of dually charged particles, angular momentum quantization leads to charge quantization only in the linear theory. Furthermore, if "strut" singularities are excluded, then isolated magnetic monopoles are forbidden in these solutions by nonlinear gravitational effects.