How Many Degrees of Freedom Has the Gluon ?

TL;DR

This paper examines whether effective gluons in glueball models should have two or three degrees of freedom, concluding that despite acquiring mass, gluons behave as massless particles with only two degrees of freedom, aligning better with lattice results.

Contribution

It compares two- and three-gluon models for glueballs and explains why gluons effectively have only two degrees of freedom despite gaining mass.

Findings

Models with two degrees of freedom better match lattice glueball spectra.

Gluons behave as massless particles with two degrees of freedom despite dynamical mass generation.

Theoretical explanation for gluon degrees of freedom in effective models.

Abstract

In constituent models, glueballs are described as bound states of effective gluons. The dynamical mass generation lead to a gluon mass without violating gauge invariance. One can then consider three degrees of freedom for those effective massive gluons. However, models with only two degrees of freedom are shown to be in better agreement with the lattice glueball spectrum. I review both models for two- and three-gluon models and explain why even though the gluon gains a mass, it behaves as a massless particle with only two degrees of freedom.