Causality Constraints on Massive Gravity

TL;DR

This paper investigates how causality constraints in de Rham-Gabadadze-Tolley massive gravity restrict the parameter space to avoid closed time-like curves, highlighting fundamental limitations of the theory.

Contribution

It demonstrates that causality considerations impose specific parameter constraints in massive gravity, ensuring the absence of closed time-like curves in pp-wave backgrounds.

Findings

Linear fluctuations exhibit time advances on pp-wave backgrounds.

Parameter space must be constrained to prevent closed time-like curves.

Classical causality violations occur within the theory's validity regime.

Abstract

The de Rham-Gabadadze-Tolley massive gravity admits pp-wave backgrounds on which linear fluctuations are shown to undergo time advances for all values of the parameters. The perturbations may propagate in closed time-like curves unless the parameter space is constrained to a line. These classical phenomena take place well within the theory's validity regime.