Surfing gravitational waves: can bigravity survive growing tensor modes?

The theory of bigravity offers one of the simplest possibilities to describe a massive graviton while having self-accelerating cosmological solutions without a cosmological constant. However, it has been shown recently that bigravity is affected by early-time fast growing modes on the tensor sector....

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Bibliographic Details
Published in:Journal of cosmology and astroparticle physics 2015-05, Vol.2015 (5), p.52-52
Main Authors: Amendola, Luca, Könnig, Frank, Martinelli, Matteo, Pettorino, Valeria, Zumalacarregui, Miguel
Format: Article
Language:English
Subjects:
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
COSMOLOGICAL CONSTANT
COSMOLOGICAL INFLATION
DISTURBANCES
GEV RANGE
GRAVITATIONAL WAVES
INFLATIONARY UNIVERSE
MATHEMATICAL SOLUTIONS
METRICS
POLARIZATION
RELICT RADIATION
TENSORS
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Summary:The theory of bigravity offers one of the simplest possibilities to describe a massive graviton while having self-accelerating cosmological solutions without a cosmological constant. However, it has been shown recently that bigravity is affected by early-time fast growing modes on the tensor sector. Here we argue that we can only trust the linear analysis up to when perturbations are in the linear regime and use a cut-off to stop the growing of the metric perturbations. This analysis, although more consistent, still leads to growing tensor modes that are unacceptably large for the theory to be compatible with measurements of the cosmic microwave background (CMB), both in temperature and polarization spectra. In order to suppress the growing modes and make the model compatible with CMB spectra, we find it necessary to either fine-tune the initial conditions, modify the theory or set the cut-off for the tensor perturbations of the second metric much lower than unity. Initial conditions such that the growing mode is sufficiently suppresed can be achieved in scenarios in which inflation ends at the GeV scale.
ISSN:1475-7516
1475-7516
DOI:10.1088/1475-7516/2015/05/052