Subleading soft dressings for QED scattering states

TL;DR

This paper investigates how Faddeev-Kulish dressings in QED scattering states suppress soft photon emissions and remove infrared divergences, especially when extended to subleading order, improving the understanding of infrared structure in quantum electrodynamics.

Contribution

It demonstrates that subleading soft dressings effectively regulate infrared divergences and suppress soft photon emissions in QED scattering processes.

Findings

Dressings remove infrared divergences order by order.

Soft-photon emission is suppressed at subleading order.

Faddeev-Kulish amplitudes match infrared-finite Fock amplitudes.

Abstract

We study soft emission in QED during scattering of Faddeev-Kulish dressed states. The incoming and outgoing charged particles are accompanied by coherent clouds of soft photons with energies below a characteristic infrared scale $E_d$. We focus on explicit processes that allow the dependence of the soft factors on the hard particles' momenta and total angular momenta to be displayed clearly. We argue that the dressings remove the infrared divergences in hard amplitudes order by order in perturbation theory, effectively regulating the contributions from virtual soft photons at the scale $E_d$. Essentially, the Faddeev-Kulish hard amplitudes become equivalent to the infrared-finite part of the corresponding Fock-basis amplitudes. Finally, tree-level soft-photon emission is found to be suppressed once the dressings are extended to subleading order in the soft-momentum expansion, as prescribed in recent work by Choi and Akhoury.