Infrared Divergences from Soft and Collinear Gauge Bosons

TL;DR

This paper reviews the Lee-Nauenberg theorem, discusses its limitations with photons in gauge theories, and reveals new soft collinear divergences that challenge the finiteness of cross-sections.

Contribution

It identifies previously overlooked soft collinear divergences in massless gauge theories and questions the assumptions behind standard divergence cancellation methods.

Findings

Standard Lee-Nauenberg approach omits certain divergences.

New soft collinear divergences are present in massless gauge theories.

Finite cross-sections require questionable assumptions.

Abstract

I review the Lee-Nauenberg thereom and discuss its inclusion of photons which are disconnected at the level of the S-matrix but connected at the level of the cross-section when there are initial and final state charged particles. I then expose a new set of soft collinear divergences in massless gauge theories which are omitted in the standard Lee-Nauenberg approach. It seems that highly questionable assumptions are needed to obtain finite cross-sections.