Dynamical constants for electromagnetic fields with elliptic-cylindrical   symmetry
  Taking into account the characteristics of a free scalar field in elliptic coordinates, a new dynamical variable is found for the free electromagnetic field. The conservation law associated to this variable cannot be obtained by direct application of standard Noether theorem since the symmetry generator is of second order. Consequences on the expected mechanical behavior of an atomic system interacting with electromagnetic waves exhibiting such a symmetry are also discussed. 
B. M. Rodr\'iguez-Lara and R. J\'auregui