Extra gauge symmetries in BHT gravity

TL;DR

This paper analyzes the canonical structure of BHT massive gravity, revealing an extra gauge symmetry at a critical point that indicates a partially massless mode, but also shows instability under linearization.

Contribution

It identifies an additional gauge symmetry at the critical point in BHT gravity, highlighting the presence of a partially massless mode and the instability of the canonical structure.

Findings

Extra gauge symmetry at the critical point

Existence of a partially massless mode

Canonical structure is unstable under linearization

Abstract

We study the canonical structure of the Bergshoeff-Hohm-Townsend massive gravity, linearized around a maximally symmetric background. At the critical point in the space of parameters, defined by $\Lambda_0/m^2=-1$, we discover an extra gauge symmetry, which reflects the existence of the partially massless mode. The number of the Lagrangian degrees of freedom is found to be 1. We show that the canonical structure of the theory at the critical point is unstable under linearization.