Theory Seminars
Manifest gauge invariance and old-fashioned perturbation theory
by
→
Europe/Madrid
IFAE Seminar Room (In-Person)
IFAE Seminar Room
In-Person
Description
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.