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- Fairbairn, Malcolm, et al.
(författare)
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Expansion history and f(R) modified gravity
- 2007
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :12, s. 005-
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Tidskriftsartikel (refereegranskat)abstract
- We attempt to fit cosmological data using f(R) modified Lagrangians containing inverse powers of the Ricci scalar varied with respect to the metric. While we can fit the supernova data well, we confirm the behaviour at medium to high redshifts reported elsewhere and argue that the easiest way to show that this class of models are inconsistent with the data is by considering the thickness of the last scattering surface. For the best fit parameters to the supernova data, the simplest 1/R model gives rise to a last scattering surface of thickness Δz~530, inconsistent with observations.
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- Fairbairn, Malcolm, et al.
(författare)
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Transparency of the Sun to gamma rays due to axionlike particles
- 2007
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 98:20, s. 201801-
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that the Sun can become partially transparent to high energy photons in the presence of a pseudoscalar. In particular, if the axion interpretation of the PVLAS result were true, then up to 2% of GeV energy gamma rays might pass through the Sun, while an even stronger effect is expected for some axion parameters. We discuss the possibilities of observing this effect. Present data are limited to the observation of the solar occultation of 3C 279 by the Energetic Gamma-Ray Experiment Telescope in 1991; 98% C.L. detection of a nonzero flux of gamma rays passing through the Sun is not yet conclusive. Since the same occultation happens every October, future experiments, e.g., the Gamma-Ray Large Area Space Telescope, are expected to have better sensitivity.
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- Rydbeck, Sara, et al.
(författare)
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Testing the DGP Model with ESSENCE
- 2007
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :05, s. 003-
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Tidskriftsartikel (refereegranskat)abstract
- We use the recent supernova data set from the ESSENCE collaboration combined with data from the Supernova Legacy Survey and nearby supernovae to test the Dvali–Gabadadze–Porrati (DGP) brane world model and its generalizations. Combination of these data with a flatness prior and the position of the peak of the cosmic microwave background (CMB) radiation disfavours the DGP model slightly. Inclusion of the baryon acoustic peak from the Sloan Digital Sky Survey increase the tension of the DGP model with the data, although it is not clear how self-consistent this procedure would be without a re-analysis of the survey data in the framework of the DGP cosmology. Generalizations of the DGP model are tested and constraints on relevant parameters obtained.
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