Accelerated expansion from ghost-free bigravity: a statistical analysis with improved generality

By Yashar Akrami, Tomi Koivisto, M. Sandstad. 2012

161 citations recorded by the source corpus.

A bstractWe study the background cosmology of the ghost-free, bimetric theory of gravity. We perform an extensive statistical analysis of the model using both frequentist and Bayesian frameworks and employ the constraints on the expansion history of the Universe from the observations of supernovae, the cosmic microwave background and the large scale structure to estimate the model’s parameters and test the goodness of the fits. We explore the parameter space of the model with nested sampling to find the best-fit chi-square, obtain the Bayesian evidence, and compute the marginalized posteriors and mean likelihoods. We mainly focus on a class of sub-models with no explicit cosmological constant (or vacuum energy) term to assess the ability of the theory to dynamically cause a late-time accelerated expansion. The model behaves as standard gravity without a cosmological constant at early times, with an emergent extra contribution to the energy density that converges to a cosmological constant in the far future. The model can in most cases yield very good fits and is in perfect agreement with the data. This is because many points in the parameter space of the model exist that give rise to time-evolution equations that are effectively very similar to those of the ΛCDM. This similarity makes the model compatible with observations as in the ΛCDM case, at least at the background level. Even though our results indicate a slightly better fit for the ΛCDM concordance model in terms of the p-value and evidence, none of the models is statistically preferred to the other. However, the parameters of the bigravity model are in general degenerate. A similar but perturbative analysis of the model as well as more data will be required to break the degeneracies and constrain the parameters, in case the model will still be viable compared to the ΛCDM.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/828e13e09ad3d443d150019683d2e7e0d9639743

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Citations in the corpus

A systematic approach to generalisations of General Relativity and their cosmological implications (2018, background): “A more promising attempt for the cosmological application was the bigravity extension of massive gravity [189, 190, 191, 192].”
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Cosmological tests of modified gravity (2015, background): “In this case, it is possible to find FRW solutions for both of the metrics [145, 146, 147].”
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Cosmology and Fundamental Physics with the Euclid Satellite (2012, background): “For instance in [26, 27] explicit selfaccelerating solutions were provided in the absence of a cosmological constant.”
The astrophysics of nanohertz gravitational waves (2018, background): “Others, especially in recent years, strive to explain an observed phenomenon that is unexplained by current physical theories, such as dark matter or dark energy (Akrami et al. 2013).”
Massive Gravity (2014, background): “2 Bi-gravity Cosmological solutions in bi-gravity have been considered in [470, 475, 104, 106, 8, 471, 474, 9, 7, 62].”
Cosmological stability bound in massive gravity and bigravity (2013, background): “One simple resolution is to look at massive gravity theories with an FRW reference metric [57] or for bigravity theories in which FRW solutions are allowed [21, 24, 24, 25, 30, 36, 47].”
Dark Energy in Light of Multi-Messenger Gravitational-Wave Astronomy (2018, result): “Flat FLRW solutions do exist, and many viable expansion histories have been found to be compatible with data (Akrami et al., 2013) and satisfying the Higuchi stability bound (Fasiello and Tolley, 2013).”