Ryan Plestid, "Topical seminar: Manifest gauge invariance and old-fashioned perturbation theory"

por Dr. Ryan Plestid (CERN)

miércoles 29 abr. 2026 10:00 → 11:30 Europe/Madrid

1001-Primera-1-1-1 - Paterna. Seminario (Universe)

When dealing with bound states (e.g., atoms or nuclei) many calculations are most efficiently carried out using old-fashioned perturbation theory. It is difficult, however, to see how gauge invariance manifests at the level of the amplitude (this is related to the non-conservation of energy in OFPT). 

In this talk I will explain how a partial-fraction trick can reorganize amplitudes into a form that is manifestly gauge invariant. Remarkably, when applied to the Compton tensor, the resulting amplitude decomposes into four separate gauge invariant pieces that are naturally organized around a heavy-mass expansion. I will comment on potential implications for atomic, nuclear, and hadronic physics applications involving QED.