Constraints on primordial isocurvature perturbations and spatial curvature by Bayesian model selection

Journal Article · Tue Dec 15 04:00:00 EST 2009 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.80.123516· OSTI ID:21313571

Vaeliviita, Jussi ^[1]; Giannantonio, Tommaso ^[2]

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1. Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 3FX (United Kingdom)
2. Argelander-Institut fuer Astronomie der Universitaet Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany)

We present posterior likelihoods and Bayesian model selection analysis for generalized cosmological models where the primordial perturbations include correlated adiabatic and cold dark matter isocurvature components. We perform nested sampling with flat and, for the first time, curved spatial geometries of the Universe, using data from the CMB anisotropies, the Union supernovae (SN) sample, and a combined measurement of the integrated Sachs-Wolfe effect. The CMB alone favors a 3% (positively correlated) isocurvature contribution in both the flat and curved cases. The nonadiabatic contribution to the observed CMB temperature variance is 0<{alpha}{sub T}<7% at 98% C.L. in the curved case. In the flat case, combining the CMB with SN data artificially biases the result towards the pure adiabatic {lambda}CDM concordance model, whereas in the curved case the favored level of nonadiabaticity stays at the 3% level with all combinations of data. However, the ratio of Bayes factors, or {delta}ln (evidence), is more than 5 points in favor of the flat adiabatic {lambda}CDM model, which suggests that the inclusion of the 5 extra parameters of the curved isocurvature model is not supported by the current data. The results are very sensitive to the second and third acoustic peak regions in the CMB temperature angular power: therefore a careful calibration of these data will be required before drawing decisive conclusions on the nature of primordial perturbations. Finally, we point out that the odds for the flat nonadiabatic model are 1:3 compared to the curved adiabatic model. This may suggest that it is not much less motivated to extend the concordance model with 4 isocurvature degrees of freedom than it is to study the spatially curved adiabatic model, though at the moment the model selection disfavors both of these models.

• OSTI ID: 21313571
• Journal Information: Physical Review. D, Particles Fields, Journal Name: Physical Review. D, Particles Fields Journal Issue: 12 Vol. 80; ISSN PRVDAQ; ISSN 0556-2821
• Country of Publication: United States
• Language: English

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