Effective Lagrangian of QED with a magnetic charge and dyon mass bounds

Abstract

The effective Lagrangian of QED coupled to dyons is calculated. The resulting generalization of the Euler-Heisenberg Lagrangian contains nonlinear $P$- 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 ${M}^{\ensuremath{-}2}$, 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.