Upper Limits on a Possible Gluon Mass

TL;DR

This paper investigates the theoretical and experimental constraints on a possible nonzero gluon mass, discussing modifications to QCD, analyzing data to set an upper limit, and exploring conceptual subtleties in interpretation.

Contribution

It provides the first comprehensive analysis of upper bounds on gluon mass considering various theoretical modifications and experimental data, highlighting interpretational challenges.

Findings

Upper limit on gluon mass is approximately 1 MeV.

Strong coupling at low energies complicates mass limit interpretation.

Fundamental differences exist between gluon mass effects and weakly coupled gauge theories.

Abstract

We analyze upper limits on a possible gluon mass, $m_g$. We first discuss various ways to modify quantum chromodynamics to include $m_g \ne 0$, including a bare mass, a Higgs mechanism, and dynamical breaking of color SU(3)$_c$. From an examination of experimental data, we infer an upper limit $m_g < O(1)$ MeV. We discuss subtleties in interpreting gluon mass limits in view of the fact that at scales below $\Lambda_{QCD}$, quantum chromodynamics is strongly coupled, perturbation theory is not reliable, and the physics is not accurately described in terms of the Lagrangian degrees of freedom, including gluons. We also point out a fundamental difference in the behavior of quantum chromodynamics with a nonzero gluon mass and a weakly coupled gauge theory with a gauge boson mass.