Massive Gravity: Exorcising the Ghost

TL;DR

This paper investigates the presence of a nonlinear ghost in Higgs massive gravity theories, showing it reappears beyond the decoupling limit and discussing modifications to eliminate it.

Contribution

It demonstrates that the nonlinear ghost reappears outside the decoupling limit and clarifies the relationship between the Vainshtein scale and ghost presence, proposing modifications to avoid ghosts.

Findings

Ghost reappears beyond the decoupling limit

No direct link between Vainshtein scale and ghost

Modifications needed to eliminate the ghost

Abstract

We consider Higgs massive gravity [1,2] and investigate whether a nonlinear ghost in this theory can be avoided. We show that although the theory considered in [10,11] is ghost free in the decoupling limit, the ghost nevertheless reappears in the fourth order away from the decoupling limit. We also demonstrate that there is no direct relation between the value of the Vainshtein scale and the existence of nonlinear ghost. We discuss how massive gravity should be modified to avoid the appearance of the ghost.