The Effective Lagrangian of QED with a Magnetic Charge and Dyon Mass Bounds

The effective Lagrangian of QED coupled to dyons is calculated. The resulting generalization of the Euler-Heisenberg Lagrangian contains non-linear P and T noninvariant terms corresponding to the virtual pair creation of dyons. The corresponding P and T violating part of the matrix element for light-by-light scattering is considered. This effect induces an electric dipole moment for the electron, of order M^{-2}, where M is the dyon mass. The current limit on the electric dipole moment of the electron yields the lower dyon mass bound M > 1 TeV.