Symmetries in nonlinear Bethe-Heitler process
  Nonlinear Bethe-Heitler process in a bichromatic laser field is investigated using strong-field QED formalism. Symmetry properties of angular distributions of created $e^-e^+$ pairs are analyzed. These properties are showed to be governed by a behavior of the vector potential characterizing the laser field, rather than by the respective electric field component. 
K. Krajewska and J. Z. Kaminski
hep-ph physics.acc-ph physics.atom-ph physics.plasm-ph