Gauge Fixing in Higher Derivative Gravity

TL;DR

This paper analyzes the gauge fixing and ghost structure in linearized four-derivative gravity, revealing the nature of physical and ghost degrees of freedom through a transformation to a second-order form.

Contribution

It introduces a method to diagonalize higher-derivative gravity, clarifying the roles of various ghosts and symmetries in the gauge fixing process.

Findings

Explicit identification of physical degrees of freedom.

Detailed structure of gauge, Weyl, and third ghosts.

Non-trivial symmetries and ghost sector peculiarities.

Abstract

Linearized four-derivative gravity with a general gauge fixing term is considered. By a Legendre transform and a suitable diagonalization procedure it is cast into a second-order equivalent form where the nature of the physical degrees of freedom, the gauge ghosts, the Weyl ghosts, and the intriguing "third ghosts", characteristic to higher-derivative theories, is made explicit. The symmetries of the theory and the structure of the compensating Faddeev-Popov ghost sector exhibit non-trivial peculiarities.