Physics of Cosmic Microwave Background anisotropies and primordial fluctuations

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

Gravitational waves from cosmological phase transitions

I discuss the generation of a stochastic background of gravitational waves during a first order phase transition. I present simple general arguments which explain the main features of the gravitational wave spectrum like the $k^3$ power law growth on large scales and a estimate for the peak amplitude. In the second part I concentrate on the electroweak phase transition and argue that the nucleosynthesis bound on its gravitational wave background seriously limits seed magnetic fields which may have been generated during this transition.Comment: 14 pages, 8 Figures Proceedeings of the 1st Mediterranean Conference on Classical and Quantum Gravity (MCCQG

Signatures of Topological Defects in the Microwave Sky: An Introduction

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

Braneworlds

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

Gauge-Transformation Properties of Cosmological Observables and its Application to the Light-Cone Average

Theoretical descriptions of observable quantities in cosmological perturbation theory should be independent of coordinate systems. This statement is often referred to as gauge-invariance of observable quantities, and the sanity of their theoretical description is verified by checking its gauge-invariance. We argue that cosmological observables are invariant scalars under diffeomorphisms and as a consequence their theoretical description is gauge-invariant, only at linear order in perturbations. Beyond linear order, they are usually not gauge-invariant, and we provide the general law for the gauge-transformation that the perturbation part of an observable does obey. We apply this finding to derive the second-order expression for the observational light-cone average in cosmology and demonstrate that our expression is indeed invariant under diffeomorphisms.Comment: 16 pages, no figures, published in JCA

What galaxy surveys really measure

In this paper we compute the quantity which is truly measured in a large galaxy survey. We take into account the effects coming from the fact that we actually observe galaxy redshifts and sky positions and not true spatial positions. Our calculations are done within linear perturbation theory for both the metric and the observer velocities but they can be used for non-linear matter power spectra. We shall see that the complications due to the fact that we only observe on our background lightcone and that we do not truly know the distance of the observed galaxy, but only its redshift is not only an additional difficulty, but even more a new opportunity for future galaxy surveys.Comment: 16 pages, 11 figures; v2: 1 table and 4 figures added showing the ratio between the new contributions and the total angular power spectrum. Accepted for publication in PRD. v3: sign typo corrected in eq. (31

Limits on stochastic magnetic fields: A defense of our paper [1]

In their recent paper ``Faraday rotation of the cosmic microwave background polarization by a stochastic magnetic field'', Kosowsky et al. Phys.Rev. D71, 043006 (2005) have commented about our paper [C.Caprini and R.Durrer, Phys. Rev. D65, 023517 (2002)], in which we derived very strong limits on the amplitude of a primordial magnetic field from gravitational wave production. They argue that our limits are erroneous. In this short comment we defend our result.Comment: 2 pages, no figure

Clarifying perturbations in the ekpyrotic universe

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

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

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