# The generalised infrared structure of the gluon propagator

## TL;DR

This paper investigates the infrared singularities of the gluon propagator in gauge theories, showing they imply on-shell states with zero norm relevant for confinement, and tests lattice QCD data for these features.

## Contribution

It provides a theoretical framework linking infrared singularities to zero-norm states and confirms their presence in lattice QCD data for the gluon propagator.

## Key findings

- Infrared singularities imply the existence of zero-norm on-shell states.
- Lattice data for the gluon propagator is consistent with these generalized poles.
- The results have implications for understanding confinement in QCD.

## Abstract

Gauge theory correlators are potentially more singular in the infrared than those in non-gauge theories. We determine the implications that these singularities have on the spectrum of the theory, proving that the appearance of generalised poles implies the existence of on-shell states with fixed mass, but zero norm. For quantum chromodynamics these poles have direct relevance for the confinement of coloured states. Using lattice data for the Landau gauge gluon propagator we subsequently test for the presence of these poles, establishing that the data is indeed consistent with such a component.