# Physics of the gluon mass gap

## TL;DR

This paper links the gluon mass gap in Landau-gauge QCD to physical observables like the confinement-deconfinement transition temperature and pion decay constant, providing a physical interpretation of the gluon mass scale.

## Contribution

It establishes a direct proportionality between the gluon mass gap and the confinement-deconfinement transition temperature, and identifies momentum regimes affecting key QCD observables.

## Key findings

- The confinement-deconfinement transition temperature is linearly proportional to the gluon mass gap.
- The gluon propagator exhibits three distinct momentum regimes with different impacts on QCD observables.
- The fit parameters of the gluon propagator have clear physical interpretations.

## Abstract

It has long been known that the gluon propagator in Landau-gauge QCD exhibits a mass gap; and its emergence has been ascribed to the action of the Schwinger mechanism in the gauge sector of QCD. In the present work, we relate this property to the physical mass gap of QCD by considering two observables associated with confinement and chiral symmetry breaking, namely the confinement-deconfinement transition temperature and the pion decay constant, respectively. It turns out that the first observable is linearly proportional to the gluon mass gap, a fact that allows us to assign a direct physical meaning to this scale. Moreover, we identify three distinct momentum regimes in the gluon propagator, ultraviolet, intermediate, and deep infrared, and assess their impact on the aforementioned observables. Both observables are sensitive to the first two regions of momenta, where functional approaches essentially coincide, but are insensitive to the third, deep infrared, regime. The combined information is used for a simple fit for the gluon propagator, all of whose parameters admit a clear physical interpretation. Finally, we discuss how this fit can help us access the intertwined dynamics of confinement and chiral symmetry breaking in QCD-type theories.