Confinement of Massive Ghost in Quadratic Gravity

TL;DR

This paper explores how massive ghosts in quadratic gravity can be confined via BRST mechanisms, potentially restoring unitarity similarly to gluon confinement in QCD.

Contribution

It demonstrates that massive ghosts can be confined through bound states and BRST symmetry, offering a novel approach to unitarity in quadratic gravity.

Findings

Massive ghosts are confined in zero-norm states via BRST quartet mechanism.

Bound states of ghosts obey a massive Klein-Gordon equation.

The scenario resembles gluon confinement in QCD.

Abstract

In the framework of the covariant canonical formalism of quadratic gravity, we consider the problem of confinement of massive ghost which violates the unitarity of the physical S-matrix. It is shown that if there is a bound state between the massive ghost and Faddeev-Popov ghost the massive ghost is confined in the zero-norm states through the BRST quartet mechanism, thereby the unitarity being restored. Based on the superfield formulation by Bonora and Tonin, we show that the asymptotic field of the massive ghost must be a massive dipole whereas that of the bound state obeys a massive Klein-Gordon equation. This situation may be of some similarity to color confinement in quantum chromodynamics (QCD) where it is conjectured that not a massless but a massive gluon is in fact confined.