Massive Gravity on de Sitter and Unique Candidate for Partially Massless Gravity

TL;DR

This paper derives the decoupling limit of massive gravity on de Sitter space, explores the partially massless limit, and introduces a unique candidate theory that propagates fewer degrees of freedom with a new Vainshtein mechanism.

Contribution

It identifies a unique non-linear candidate for partially massless gravity and analyzes the decoupling limit, revealing a new Vainshtein mechanism and continuity between massive and partially massless gravity.

Findings

A decoupling theory similar to Minkowski case.

Existence of a unique fully non-linear partially massless candidate.

A new Vainshtein mechanism at m^2→2H^2.

Abstract

We derive the decoupling limit of Massive Gravity on de Sitter in an arbitrary number of space-time dimensions d. By embedding d-dimensional de Sitter into d+1-dimensional Minkowski, we extract the physical helicity-1 and helicity-0 polarizations of the graviton. The resulting decoupling theory is similar to that obtained around Minkowski. We take great care at exploring the partially massless limit and define the unique fully non-linear candidate theory that is free of the helicity-0 mode in the decoupling limit, and which therefore propagates only four degrees of freedom in four dimensions. In the latter situation, we show that a new Vainshtein mechanism is at work in the limit m^2\to 2 H^2 which decouples the helicity-0 mode when the parameters are different from that of partially massless gravity. As a result, there is no discontinuity between massive gravity and its partially massless limit, just in the same way as there is no discontinuity in the massless limit of massive gravity. The usual bounds on the graviton mass could therefore equivalently well be interpreted as bounds on m^2-2H^2. When dealing with the exact partially massless parameters, on the other hand, the symmetry at m^2=2H^2 imposes a specific constraint on matter. As a result the helicity-0 mode decouples without even the need of any Vainshtein mechanism.