Description
As the attainable strength of electromagnetic fields in the lab increases, so too does the access to higher-order strong-field QED processes. On the one hand, the 'long-pulse approximation' used throughout numerical simulations justifies replacing second-order processes such as nonlinear trident with sequential first-order subprocesses where the intermediate photon is real and propagates. On the other hand, experimental results from the NA63 experiment of electronic nonlinear trident process in oriented crystals indicate a signal produced by the one-step process where the intermediate photon remains virtual. Motivated by these results, we revisit the question of separation into one- and two-step processes by studying the toy model of an electron-positron pair produced by a muon scattering in an intense electromagnetic field. Using the locally monochromatic approximation (LMA), we investigate the conditions required for obtaining the two-step limit and how one may efficiently include contributions from the one-step process in calculations.
