The Veneziano ghost, glost and gauge copies in QCD

TL;DR

This paper revisits a proposal linking the Veneziano ghost to gluon confinement in QCD, discussing gauge invariance issues and providing a Landau gauge example that isolates the ghost's effects.

Contribution

It critically examines the gauge invariance of the Veneziano ghost coupling and offers a Landau gauge model that isolates the ghost's role without altering the gluon propagator.

Findings

The coupling's gauge dependence raises subtleties in the proposal.

A Landau gauge example shows the ghost's effects can be decoupled from the gluon propagator.

The proposal's implications for color confinement are discussed.

Abstract

In this short note, we come back to the recent proposal put forward by Kharzeev and Levin [PRL 114 (2015) 24, 242001], in which they phenomenologically couple the non-perturbative Veneziano ghost to the perturbative gluon, leading to a modified gluon propagator (the "glost") of the Gribov type, with complex poles. As such, a possible link was made between the QCD topological \theta-vacuum (Veneziano ghost) and color confinement (no physically observable gluons). We discuss some subtleties concerning gauge (BRST) invariance of this proposal, related to the choice of Feynman gauge. We furthermore provide an example in the Landau gauge of a similar phenomenological vertex that also describes the necessary Veneziano ghost but does not affect the Landau gauge gluon propagator.