329 research outputs found


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    This course is an introduction to the physics of braneworlds. We concentrate on braneworlds with only one extra-dimension and discuss their gravity. We derive the gravitational equations on the brane from the bulk Einstein equation and explore some limits in which they reduce to 4-dimensional Einstein gravity. We indicate how cosmological perturbations from braneworlds are probably very different from usual cosmological perturbations and give some examples of the preliminary results in this active field of research. For completeness, we also present an introduction to 4-dimensional cosmological perturbation theory and, especially its application to the anisotropies of the cosmic microwave background.Comment: 39 pages, 12 Figures, course given at the XI Brazilian School of Cosmology and Gravitatio

    Physics of Cosmic Microwave Background anisotropies and primordial fluctuations

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    The physics of the origin and evolution of CMB anisotropies is described. I explain the idea and status of cosmic parameter estimation and follow it up with critical comments on its dependence on model assumptions and initial conditions.Comment: 13 pages, 6 figs. Talk given at "Matter in the Universe", ISSI Ber

    Clarifying perturbations in the ekpyrotic universe

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    In this note I try to clarify the problem of perturbations in the ekpyrotic universe. I write down the most general matching conditions and specify the choices taken by the two debating sides. I also bring up the problem of surface stresses which always have to be present when a transition from a collapsing to an expanding phase is made.Comment: 3 pages, no figures Some typo's and a conceptial mistake corrected. Conclusions unaltere

    Signatures of Topological Defects in the Microwave Sky: An Introduction

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    An introduction to topological defects in cosmology is given. We discuss their possible relevance for structure formation. Especial emphasis is given on the signature of topological defects in the spectrum of anisotropies in the cosmic microwave background. We present simple analytic estimates for the CMB spectrum on large and intermediate scales and compare them with the corresponding approximations for models where initial perturbations are generated during an inflationary epoch.Comment: LaTex file 18pages, 5 postscript figures Contribution to the Proceedings of the conference on 'Topolocigal Defects in Cosmology' in Roma, La Sapienz

    Cosmic Microwave Background Anisotropies from Scaling Seeds: Generic Properties of the Correlation Functions

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    In this work we present a partially new method to analyze fluctuations which are induced by causal scaling seeds. We show that the power spectra due to this kind of seed perturbations are determined by five analytic functions, which we determine numerically for a special example. We put forward the view that, even if recent work disfavors the models with cosmic strings and global O(4) texture, causal scaling seed perturbations merit a more thorough and general analysis, which we initiate in this paper.Comment: LaTeX file with RevTex, 6 pages, 6 PS figs., submitted to Phys. Rev. D. A version with higher quality images can be found at http://mykonos.unige.ch/~kunz
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