Journal
PHYSICS LETTERS B
Volume 748, Issue -, Pages 37-44Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.physletb.2015.06.062
Keywords
Modified gravity; Massive gravity; Background cosmology; Cosmic acceleration; Dark energy; Bimetric gravity; Bigravity
Funding
- DFG through the project TRR33 The Dark Universe
- Graduate College Astrophysics of Fundamental Probes of Gravity
- ERC grant under the FP7 [615203]
- Swiss National Science Foundation through the NCCR SwissMAP
- STFC
- STFC [ST/M00418X/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/M00418X/1] Funding Source: researchfish
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Bimetric theory describes gravitational interactions in the presence of an extra spin-2 field. Previous work has suggested that its cosmological solutions are generically plagued by instabilities. We show that by taking the Planck mass for the second metric, M-f, to be small, these instabilities can be pushed back to unobservably early times. In this limit, the theory approaches general relativity with an effective cosmological constant which is, remarkably, determined by the spin-2 interaction scale. This provides a late-time expansion history which is extremely close to Lambda CDM, but with a technically-natural value for the cosmological constant. We find M-f should be no larger than the electroweak scale in order for cosmological perturbations to be stable by big-bang nucleosynthesis. We further show that in this limit the helicity-0 mode is no longer strongly-coupled at low energy scales. (C) 2015 The Authors. Published by Elsevier B.V.
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