Journal Article

Should we doubt the cosmological constant?

M. C. March, G. D. Starkman, R. Trotta and P. M. Vaudrevange

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 410, issue 4, pages 2488-2496
Published in print February 2011 | ISSN: 0035-8711
Published online January 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17614.x
Should we doubt the cosmological constant?

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While Bayesian model selection is a useful tool to discriminate between competing cosmological models, it only gives a relative rather than an absolute measure of how good a model is. Bayesian doubt introduces an unknown benchmark model against which the known models are compared, thereby obtaining an absolute measure of model performance in a Bayesian framework. We apply this new methodology to the problem of the dark energy equation of state, comparing an absolute upper bound on the Bayesian evidence for a presently unknown dark energy model against a collection of known models including a flat Lambda cold dark matter (ΛCDM) scenario. We find a strong absolute upper bound to the Bayes factor B between the unknown model and ΛCDM, giving B≲ 5. The posterior probability for doubt is found to be less than 13 per cent (with a 1 per cent prior doubt) while the probability for ΛCDM rises from an initial 25 per cent to almost 70 per cent in light of the data. We conclude that ΛCDM remains a sufficient phenomenological description of currently available observations and that there is little statistical room for model improvement.

Keywords: methods: statistical; supernovae: type Ia; cosmological parameters; dark energy

Journal Article.  8239 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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