Action Principle for the Classical Dual Electrodynamics
  The purpose of this paper is to formulate an action principle which allows for the construction of a classical lagrangean including both electric and magnetic currents. The lagrangean is non-local and shown to yield all the expected (local) equations for dual electrodynamics. 
P.C.R. Cardoso de Mello, S. Carneiro and M.C. Nemes