Elecromagnetic Duality on the Light-Front in the Presence of External   Sources
  We investigate the issue of electromagnetic duality on the light front. We work with Zwanziger's theory of electric and magnetic sources which is appropriate for treating duality. When quantized on the light-front in the light front gauge, this theory yields two independent phase space degrees of freedom, namely the two transverse field components, the right number to describe the gauge field sector of normal light-front QED and also the appropriate commutator between them. The electromagnetic duality transformation formulated in terms of them is similar in form to the Susskind transformation proposed for the free theory, provided one identifies them as the dynamical field components of the photon on the light-front in the presence of magnetic sources. The Hamiltonian density written in terms of these components is invariant under the duality transformation. 
Asmita Mukherjee and Somdatta Bhattacharya