On the effective action of a dual Dirac string in a classical model

The effective action of a dual Dirac string is determined within a 4-dimensional formulation of Diracʹs extension of Electro-dynamics supplemented by the dual London equation of superconductivity. We identify the effective action calculated for classical electromagnetic fields induced by a dual Dirac string with the string action and evaluate the string tension. Our string action differs from that found by Nambu.