Problems of Massive Gravities

TL;DR

This paper reviews the method of characteristics in the context of massive gravity theories, highlighting fundamental issues like superluminality and acausality that challenge their physical viability, and extends no-go results across all parameter ranges.

Contribution

It provides a comprehensive analysis of the limitations of massive gravity models using the method of characteristics, including an extension of no-go results to all parameter ranges.

Findings

Massive gravity models exhibit superluminal signals and acausality.

The entire three-parameter space of these theories faces fundamental consistency issues.

Bimetric models are also shown to suffer similar problems.

Abstract

The method of characteristics is a key tool for studying consistency of equations of motion; it allows issues such as predictability, maximal propagation speed, superluminality, unitarity and acausality to be addressed without requiring explicit solutions. We review this method and its application to massive gravity theories to show the limitations of these models' physical viability: Among their problems are loss of unique evolution, superluminal signals, matter coupling inconsistencies and micro-acausality (propagation of signals around local closed timelike/causal curves). We extend previous no-go results to the entire three-parameter range of massive gravity theories. It is also argued that bimetric models suffer a similar fate.