Massive Gravity Acausality Redux

TL;DR

This paper confirms that massive gravity models exhibit superluminal propagation and acausality through explicit characteristic matrix analysis, highlighting fundamental issues in their theoretical consistency.

Contribution

It provides a first order characteristic matrix computation that explicitly demonstrates superluminal propagation and acausality in massive gravity.

Findings

Massive gravity exhibits superluminal propagation.

Explicit analysis confirms acausality in massive gravity.

First order shock analysis aligns with previous second order results.

Abstract

Massive gravity (mGR) is a 5(=2s+1) degree of freedom, finite range extension of GR. However, amongst other problems, it is plagued by superluminal propagation, first uncovered via a second order shock analysis. First order mGR shock structures have also been studied, but the existence of superluminal propagation in that context was left open. We present here a concordance of these methods, by an explicit (first order) characteristic matrix computation, which confirms mGR's superluminal propagation as well as acausality.