Cosmological stability bound in massive gravity and bigravity

We give a simple derivation of a cosmological bound on the graviton mass for spatially flat FRW solutions in massive gravity with an FRW reference metric and for bigravity theories. This bound comes from the requirement that the kinetic term of the helicity zero mode of the graviton is positive defi...

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Bibliographic Details
Published in:Journal of cosmology and astroparticle physics 2013-12, Vol.2013 (12), p.i-36
Main Authors: Fasiello, Matteo, Tolley, Andrew J
Format: Article
Language:English
Subjects:
ACCELERATION
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Cosmology
DECOUPLING
Derivation
EQUATIONS
EXPANSION
Flats
GRAVITATION
Gravitons
HELICITY
Mathematical analysis
Mathematical models
MATHEMATICAL SOLUTIONS
METRICS
POTENTIALS
STABILITY
SYMMETRY
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Summary:We give a simple derivation of a cosmological bound on the graviton mass for spatially flat FRW solutions in massive gravity with an FRW reference metric and for bigravity theories. This bound comes from the requirement that the kinetic term of the helicity zero mode of the graviton is positive definite. The bound is dependent only on the parameters in the massive gravity potential and the Hubble expansion rate for the two metrics. We derive the decoupling limit of bigravity and FRW massive gravity, and use this to give an independent derivation of the cosmological bound. We recover our previous results that the tension between satisfying the Friedmann equation and the cosmological bound is sufficient to rule out all observationally relevant FRW solutions for massive gravity with an FRW reference metric. In contrast, in bigravity this tension is resolved due to different nature of the Vainshtein mechanism. We find that in bigravity theories there exists an FRW solution with late-time self-acceleration for which the kinetic terms for the helicity-2, helicity-1 and helicity-0 are generically nonzero and positive making this a compelling candidate for a model of cosmic acceleration. We confirm that the generalized bound is saturated for the candidate partially massless (bi)gravity theories but the existence of helicity-1/helicity-0 interactions implies the absence of the conjectured partially massless symmetry for both massive gravity and bigravity.
ISSN:1475-7516
1475-7516
DOI:10.1088/1475-7516/2013/12/002