Infrared problem in quantum electrodynamics

Abstract: The infrared problem in quantum electrodynamics consists of intriguing difficulties in scattering theory appearing at large scales and low energies. Although they can be circumvented using ad hoc recipes, such as the inclusive collision cross sections, there have been continuing efforts to reach a conceptually clear and mathematically rigorous understanding. In this article we focus on such developments of the last two decades. We start from the Buchholz-Roberts approach in the setting of algebraic QFT, which is based on the idea that there should be no infrared problems inside the future lightcone. Then we move on to the setting of non-relativistic QED, where insights from Haag-Ruelle scattering theory and the Faddeev-Kulish formalism suggest concrete formulas for the physical electron. Finally, in a setting of perturbative QFT, we outline a recent proposal for an infrared finite scattering matrix, which is also in the spirit of the Faddeev-Kulish approach.