The processes of electron-positron annihilation into photon pairs and of pair creation by photons are of interest both theoretically and experimentally. ... This should come as some surprise since you probably know that by crossing you should expect each of the two Compton diagrams to give rise to one Feynman diagram for the annihilation process (see, for instance, [ 2 ] Section 7.8, [ 1 ] Section 6.15). ... see section ) and hence get the following formula for the total cross section: . ...