Problems of Massive Gravities

Understand

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.