High-energy electroproduction in an atomic field

We discuss the most recent results in studies of high-energy electroproduction in an atomic field. Production of an $\rm e^+e^-$ pair by a relativistic electron, relativistic muon, or light nucleus and production of a $\mu ^+\mu ^-$ pair by a relativistic electron are reviewed. We focus on an accurate account of the interaction of the incoming particle and produced pair with the atomic field (Coulomb corrections). In all the considered cases, interaction of the particle that produces a virtual photon with the atomic field is shown to significantly change the differential cross section of the process (differential with respect to the momentum of the photon-emitting particle), in disagreement with the generally accepted opinion. However, the process cross section integrated over that momentum is only weakly affected by the interaction. Pair production in an unbound or bound state (positronium, muonium, and dimuonium) is discussed.