Constraints on the cosmological density parameters and cosmic topology

A nontrivial topology of the spatial section of the universe is an observable, which can be probed for all locally homogeneous and isotropic universes, without any assumption on the cosmological density parameters. We discuss how one can use this observable to set constraints on the density parameters of the Universe by using a specific spatial topology along with type Ia supenovae and X-ray gas mass fraction data sets.Comment: 11 pages, 4 figures. To appear in Int. J. Mod. Phys. D (2006). Invited talk delivered at the 2nd International Workshop on Astronomy and Relativistic Astrophysic

Non-Gaussianity in the HILC foreground-reduced three-year WMAP CMB map

A detection or nondetection of primordial non-Gaussianity in the CMB data is essential not only to test alternative models of the physics of the early universe but also to discriminate among classes of inflationary models. Given this far reaching consequences of such a non-Gaussianity detection for our understanding of the physics of the early universe, it is important to employ alternative indicators in order to have further information about the Gaussianity features of CMB that may be helpful for identifying their origins. In this way, a considerable effort has recently gone into the design of non-Gaussianity indicators, and in their application in the search for deviation from Gaussianity in the CMB data. Recently we have proposed two new large-angle non-Gaussianity indicators which provide measures of the departure from Gaussianity on large angular scales. We have used these indicators to carry out analyses of Gaussianity of the single frequency bands and of the available foreground-reduced {\it five-year} maps with and without the KQ75 mask. Here we extend and complement these studies by performing a new analysis of deviation from Gaussianity of the {\it three-year} harmonic ILC (HILC) foreground-reduced full-sky and KQ75 masked maps obtained from WMAP data. We show that this full-sky foreground-reduced maps presents a significant deviation from Gaussianity, which is brought down to a level of consistency with Gaussianity when the KQ75 mask is employed.Comment: 6 pages, 1 figure. To appear in IJMPD (2010). V2: Corrected ref.[8]

A note on the large-angle anisotropies in the WMAP cut-sky maps

Recent analyses of the WMAP data seem to indicate the possible presence of large-angle anisotropy in the Universe. If confirmed, these can have important consequences for our understanding of the Universe. A number of attempts have recently been made to establish the reality and nature of such anisotropies in the CMB data. Among these is a directional indicator recently proposed by the authors. A distinctive feature of this indicator is that it can be used to generate a sky map of the large-scale anisotropies of the CMB maps. Applying this indicator to full-sky temperature maps we found a statistically significant preferred direction. The full-sky maps used in these analyses are known to have residual foreground contamination as well as complicated noise properties. Thus, here we performed the same analysis for a map where regions with high foreground contamination were removed. We find that the main feature of the full-sky analysis, namely the presence of a significant axis of asymmetry, is robust with respect to this masking procedure. Other subtler anomalies of the full-sky are on the other hand no longer present.Comment: 10 pages, 3 figeres. We performed a similar analysis of arXiv:astro-ph/0511666 by considering the LILC map with a Kp2 sky cut, and find that the presence of a significant axis of asymmetry is robust with respect to this masking procedur

Observational constraints on modified gravity models and the Poincar\'e dodecahedral topology

We study the constraints that spatial topology may place on the parameters of models that account for the accelerated expansion of the universe via infrared modifications to general relativity, namely the Dvali-Gabadadze-Porrati braneworld model as well as the Dvali-Turner and Cardassian models. By considering the Poincar\'e dodecahedral space as the circles-in-the-sky observable spatial topology, we examine the constraints that can be placed on the parameters of each model using type Ia supernovae data together with the baryon acoustic peak in the large scale correlation function of the Sloan Digital Sky Survey of luminous red galaxies and the Cosmic Microwave Background Radiation shift parameter data. We show that knowledge of spatial topology does provide relevant constraints, particularly on the curvature parameter, for all models.Comment: Revtex4, 10 pages, 1 table, 12 figures; version to match the one to be published in Physical Review

Summary Talk on Cosmology and Gravitation: XXII Brazilian National Meeting on Particles and Fields

The plenary lectures, parallel talks, oral presentations and panel contributions on Cosmology and Gravitation presented during the XXII Brazilian National Meeting on Particles and Fields are briefly reviewed. Some remarks on the area are also presented

Segre Types of Symmetric Two-tensors in n-Dimensional Spacetimes

Three propositions about Jordan matrices are proved and applied to algebraically classify the Ricci tensor in n-dimensional Kaluza-Klein-type spacetimes. We show that the possible Segre types are [1,1...1], [21...1], [31\ldots 1], [z\bar{z}1...1] and degeneracies thereof. A set of canonical forms for the Segre types is obtained in terms of semi-null bases of vectors.Comment: 14 pages, LaTeX, replaced due to a LaTex erro

Circles-in-the-sky searches and observable cosmic topology in the inflationary limit

While the topology of the Universe is at present not specified by any known fundamental theory, it may in principle be determined through observations. In particular, a non-trivial topology will generate pairs of matching circles of temperature fluctuations in maps of the cosmic microwave background, the so-called circles-in-the-sky. A general search for such pairs of circles would be extremely costly and would therefore need to be confined to restricted parameter ranges. To draw quantitative conclusions from the negative results of such partial searches for the existence of circles we need a concrete theoretical framework. Here we provide such a framework by obtaining constraints on the angular parameters of these circles as a function of cosmological density parameters and the observer's position. As an example of the application of our results, we consider the recent search restricted to pairs of nearly back-to-back circles with negative results. We show that assuming the Universe to be very nearly flat, with its total matter-energy density satisfying the bounds $0 <|\Omega_0 - 1| \lesssim 10^{-5}$, compatible with the predictions of typical inflationary models, this search, if confirmed, could in principle be sufficient to exclude a detectable non-trivial cosmic topology for most observers. We further relate explicitly the fraction of observers for which this result holds to the cosmological density parameters.Comment: 8 pages, 4 figures. V2: Version to appear in Phys. Rev. D (2008), typos corrected, references adde

Generalized Chaplygin gas model, supernovae and cosmic topology

In this work we study to which extent the knowledge of spatial topology may place constraints on the parameters of the generalized Chaplygin gas (GCG) model for unification of dark energy and dark matter. By using both the Poincar\'e dodecahedral and binary octahedral spaces as the observable spatial topologies, we examine the current type Ia supernovae (SNe Ia) constraints on the GCG model parameters. We show that the knowledge of spatial topology does provide additional constraints on the $A_s$ parameter of the GCG model but does not lift the degeneracy of the $\alpha$ parameter.Comment: Revtex 4, 8 pages, 10 figures, 1 table; version to match the published on

Signature for the Shape of the Universe

If the universe has a nontrivial shape (topology) the sky may show multiple correlated images of cosmic objects. These correlations can be couched in terms of distance correlations. We propose a statistical quantity which can be used to reveal the topological signature of any Robertson-Walker (RW) spacetime with nontrivial topology. We also show through computer-aided simulations how one can extract the topological signatures of flat, elliptic, and hyperbolic RW universes with nontrivial topology.Comment: 11 pages, 3 figures, LaTeX2e. This paper is a direct ancestor of gr-qc/9911049, put in gr-qc archive to make it more accessibl