Novel symmetries in Weyl-invariant gravity with massive gauge field

TL;DR

This paper explores the symmetries of Weyl-invariant scalar-tensor gravity with a massive gauge field, revealing new symmetries and methods to remove unphysical ghost states through symmetry combinations.

Contribution

It identifies novel symmetries in Weyl-invariant gravity with a massive gauge field and demonstrates how combining these symmetries eliminates unphysical ghost states.

Findings

Quadratic Lagrangian respects both diffeomorphism and Weyl symmetries in Minkowski background.

Negative norm states exist but can be decoupled by symmetry combination.

Scalar field modifies gauge conditions without becoming a dynamic mode.

Abstract

The background field method is used to linearize the Weyl invariant scalar-tensor gravity, coupled with a Stueckelberg field. For a generic background metric, this action is found to be not invariant, under both diffeomorphism and generalized Weyl symmetry, the latter being a combination of gauge and Weyl transformations. Interestingly, the quadratic Lagrangian, emerging from a background of Minkowski metric, respects both the transformations, independently. Becchi-Rouet-Stora-Tyutin (BRST) symmetry of scalar-tensor gravity coupled with a Stueckelberg-like massive gauge particle, possessing diffeomorphism and generalized Weyl symmetry, reveals that in both the cases, negative norm states with unphysical degrees of freedom do exist. We then show that, by combining diffeomorphism and generalized Weyl symmetries, all the ghost states decouple, thereby removing the unphysical redundancies of the theory. During this process, the scalar field does not represent any dynamic mode, yet modifies the usual harmonic gauge condition through non-minimal coupling with gravity.