Graviton propagation in ghost-free massive gravity
Claudia de Rham, Jan Kożuszek, Andrew J. Tolley, Toby Wiseman
TLDR
This paper proves that helicity-2 gravitons in dRGT massive gravity always propagate on the metric lightcone, crucial for observational tests.
Key contributions
- Analyzes ghost-free dRGT massive gravity with two of its three possible mass terms.
- Identifies five gravitational degrees of freedom, including helicity-2, -1, and -0 modes.
- Proves helicity-2 gravitons always propagate on the metric lightcone for any background.
- Crucial for current and future observational tests of massive gravity theories.
Why it matters
This paper resolves a key question about graviton propagation in massive gravity. Understanding how helicity-2 modes behave is vital for validating the theory against observations. It provides a foundational result for future experimental tests.
Original Abstract
We consider the ghost-free dRGT massive gravity with two of its three possible mass terms. This theory has five gravitational degrees of freedom. On Minkowski spacetime these modes have helicity-2, -1 and -0 and propagate on the Minkowski lightcone in the high-frequency limit. However for a general background the degrees of freedom corresponding to the helicity-1 and -0 modes have characteristics different to that of the metric lightcone. Here we prove in all generality, that the two degrees of freedom corresponding to the helicity-2 mode always propagate on the metric lightcone for any background in the high-frequency limit, which has significant relevance for current and future observational tests of the theory.
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