"Depletion and Focusing in Strong-Field Scattering"

When studying scattering amplitudes in quantum field theory, we usually operationalize their calculation in terms of a perturbative expansion around a trivial field configuration. This assumption is certainly good enough to capture many important phenomena, but there are also many scenarios (e.g., intense light-light interactions, heavy ion collisions, early universe physics) where it is not well justified. Experimental setups probing many of these scenarios require the computation of scattering amplitudes in strong (i.e., non-trivial, non-perturbative) background fields to make meaningful theoretical predictions. However, most of the impressive toolkit that has been built for standard perturbative amplitudes over the last 30 years fails in even the simplest strong backgrounds. In this talk, I will discuss how progress can be made on two notoriously difficult features — depletion and spatial focusing effects — in the specific context of strong-field scattering in QED.