An imaginary part of the zero angle light-by-light scattering tensor

Abstract

We calculate the bilinear combination of Dirac tensors describing the creation of a pair of charged particles (pi-meson or leptons) by virtual photons integrated on the final particle phase volume. It can be interpreted as an s channel discontinuity of the zero angle light-by-light scattering tensor with both photons off-mass shell. The expression of the light-by-light scattering tensor is represented in the form where the gauge invariance and the Bose symmetry are explicitly shown. Some applications and the checks are discussed.