QED Effective Action in Magnetic Field Backgrounds and Electromagnetic   Duality
  In the in-out formalism we advance a method of the inverse scattering matrix for calculating effective actions in pure magnetic field backgrounds. The one-loop effective actions are found in a localized magnetic field of Sauter type and approximately in a general magnetic field by applying the uniform semiclassical approximation. The effective actions exhibit the electromagnetic duality between a constant electric field and a constant magnetic field and between $E(x) = E sech^2 (x/L)$ and $B(x) = B sech^2 (x/L)$. 
Sang Pyo Kim (Kunsan Nat'l Univ., Nat'l Taiwan Univ., and YITP, Kyoto   Univ.)
hep-th astro-ph.HE hep-ph nucl-th