286 research outputs found

    The CMBR Spectrum

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    A short review of the measured spectrum of the Cosmic Microwave Background Radiation (CMBR) and implications. Extensions of the Kompaneets equation and Sunyaev-Zel'dovich effect are given.Comment: 30 pages, 9 figures from lectures at NATO ASI "The Cosmic Microwave Background" Strasbourg 199

    Confirmation of the Copernican principle at Gpc radial scale and above from the kinetic Sunyaev Zel'dovich effect power spectrum

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    The Copernican principle, a cornerstone of modern cosmology, remains largely unproven at Gpc radial scale and above. Here we will show that, violations of this type will inevitably cause a first order anisotropic kinetic Sunyaev Zel'dovich (kSZ) effect. If large scale radial inhomogeneities have amplitude large enough to explain the "dark energy" phenomena, the induced kSZ power spectrum will be much larger than the ACT/SPT upper limit. This single test confirms the Copernican principle and rules out the adiabatic void model as a viable alternative to dark energy.Comment: 4 pages, 2 figures. v2: updated with ACT result. v3: updated with SPT result. Expanded discussions. Accepted to PR

    Perturbations from cosmic strings in cold dark matter

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    A systematic linear analysis of the perturbations induced by cosmic strings in cold dark matter is presented. The power spectrum is calculated and it is found that the strings produce a great deal of power on small scales. It is shown that the perturbations on interesting scales are the result of many uncorrelated string motions, which indicates a much more Gaussian distribution than was previously supposed

    Perturbations from strings don't look like strings!

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    A systematic analysis is challenging popular ideas about perturbation from cosmic strings. One way in which the picture has changed is reviewed. It is concluded that, while the scaling properties of cosmic strings figure significantly in the analysis, care must be taken when thinking in terms of single time snapshots. The process of seeding density perturbations is not fundamentally localized in time, and this fact can wash out many of the details which appear in a single snapshot

    Cold + Hot Dark Matter and the Cosmic Microwave Background

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    We examine the cosmic microwave background power spectrum for adiabatic models with a massive neutrino component. We present the results of a detailed numerical evolution of cold + hot dark matter (CHDM) models and compare with the standard cold dark matter (CDM) spectrum. The difference is of order 5−105-10% for 400<l<1000400 < l < 1000 for currently popular CHDM models. With semi-analytic approximations, we also discuss the relevant physics involved. Finally we remark on the ability of future experiments to differentiate between these models. An all-sky experiment with a beam size smaller than 30 arcminutes can distinguish between CHDM and CDM if other cosmological parameters are known. Even allowing other parameters to vary, it may be possible to distinguish CDM from CHDM.Comment: Compressed uuencoded postscript, 26 pages including figures. Color version available at http://www-astro-theory.fnal.gov

    Generation of Isocurvature from Curvature Inhomogeneities on Super-Horizon Scales

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    Here it is shown 1) how isocurvature inhomogeneities correlated on causally disconnected (super-horizon) scales are generated from curvature inhomogeneities which are known to be correlated on these scales 2) that super-horizon isocurvature generation is nearly inevitable for non-equilibrium chemical processes 3) that the amplitude of the compositional isocurvature correlations a) can be large for production of rare objects, b) falls off rapidly with separation c) falls off at scales below the horizon when these modes are generated. These two fall-offs results in an "isocurvature bump" in the power spectrum. Isocurvature generation is illustrated by the process of dark matter freeze-in, computed here with both separate universe modelling and linear perturbation theory. For freeze-in the most prominent isocurvature modes are inhomogeneities in the ratio of dark matter to standard model matter. Much smaller inhomogeneities in the ratio of baryons to standard model entropy are also produced. Previous constraints on freeze-in from Ly-α\alpha clouds limit the bump enhancement to ≲10%\lesssim10\% on comoving scales ≲1 \lesssim1\,Mpc. Current observations are not sensitive to the isocurvature modes generated in viable freeze-in models. Results are obtained using a somewhat novel framework to describe cosmological inhomogeneities.Comment: 22 pages 2 figures. Composed as Mathematica notebook. Will be migrated to LaTeX in future version
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