81 research outputs found

    The Signature of Proper Motion in the Microwave Sky

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    The cosmic microwave background radiation defines a preferred cosmic rest frame, and inflationary cosmological theories predict that the microwave background temperature fluctuations should be statistically isotropic in this rest frame. For observers moving with respect to the rest frame, the temperature fluctuations will no longer be isotropic, due to the preferred direction of motion. The most prominent effect is a dipole temperature variation, which has long been observed with an amplitude of a part in a thousand of the mean temperature. An observer's velocity with respect to the rest frame will also induce changes in the angular correlation function and creation of non-zero off-diagonal correlations between multipole moments. We calculate both of these effects, which are part-in-a-thousand corrections to the rest frame power spectrum and correlation function. Both should be detectable in future full-sky microwave maps from the Planck satellite. These signals will constrain cosmological models in which the cosmic dipole arises partly from large-scale isocurvature perturbations, as suggested by recent observations.Comment: 5 pages, no figures. Submitted to Physical Review Letter

    Microwave Background Anisotropies from Alfven waves

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    We investigate microwave background anisotropies in the presence of primordial magnetic fields. We show that a homogeneous field with fixed direction can amplify vector perturbations. We calculate the correlations of δT/T\delta T/T explicitly and show that a large scale coherent field induces correlations between aℓ−1,ma_{\ell-1,m} and aℓ+1,ma_{\ell+1,m}. We discuss constraints on amplitude and spectrum of a primordial magnetic field imposed by observations of CMB anisotropies.Comment: 18 page LaTeX file, 4 postscript figs. included, submitted to PR

    The observational constraints on the flat Ï•\phiCDM models

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    Most dark energy models have the Λ\LambdaCDM as their limit, and if future observations constrain our universe to be close to Λ\LambdaCDM Bayesian arguments about the evidence and the fine-tuning will have to be employed to discriminate between the models. Assuming a baseline Λ\LambdaCDM model we investigate a number of quintessence and phantom dark energy models, and we study how they would perform when compared to observational data, such as the expansion rate, the angular distance, and the growth rate measurements, from the upcoming Dark Energy Spectroscopic Instrument (DESI) survey. We sample posterior likelihood surfaces of these dark energy models with Monte Carlo Markov Chains while using central values consistent with the Planck Λ\LambdaCDM universe and covariance matrices estimated with Fisher information matrix techniques. We find that for this setup the Bayes factor provides a substantial evidence in favor of the Λ\LambdaCDM model over most of the alternatives. We also investigated how well the CPL parametrization approximates various scalar field dark energy models, and identified the location for each dark energy model in the CPL parameter space.Comment: 11 pages, 5 figures; 4 tables; published in European Journal of Physics
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