Mapping the large-scale anisotropy in the WMAP data

Abstract

Aims. Analyses of recent cosmic microwave background (CMB) observations have provided increasing hints that there are deviations in the universe from statistical isotropy on large scales. Given the far reaching consequences of such an anisotropy for our understanding of the universe, it is important to employ alternative indicators in order to determine whether the reported anisotropy is cosmological in origin and, if so, extract information that may be helpful for identifying its causes. Methods. Here we propose a new directional indicator, based on separation histograms of pairs of pixels, which provides a measure of departure from statistical isotropy. The main advantage of this indicator is that it generates a sky map of large-scale anisotropies in the CMB temperature map, thus allowing a possible additional window into their causes. Results. Using this indicator, we find statistically significant excess of large-scale anisotropy at well over the 95% confidence level. This anisotropy defines a preferred direction in the CMB data. We discuss the statistical significance of this direction compared to Monte Carlo data obtained under the statistical isotropy hypothesis, and also compare it with other such axes recently reported in the literature. In addition we show that our findings are robust with respect to the details of the method used, so long as the statistical noise is kept under control; and they remain unchanged compared to the foreground cleaning algorithms used in CMB maps. We also find that the application of our method to the first and three-year WMAP data produces similar results.

String Theory Explanation of Large-Scale Anisotropy and Anomalous Alignment

“…They detected anomalies in the CMB, including large-scale anisotropies, non-Gaussian distributions, and anomalous alignments. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Current in°a-tion theory can explain short-range anisotropies in the microwave background radiation, but it fails to explain large-scale anisotropies.…”

Hemispherical power asymmetry: parameter estimation from cosmic microwave background WMAP5 data

“…Their statistical properties are imprinted in the CMB fluctuations, providing an interesting window on the processes of the early Universe. Although the instrumental effects, like non-Gaussian and non-isotropic noise, or eccentric beams, and astrophysical foregrounds effects, like Galactic, and extra-Galactic point sources, and extended sources of emission, are either well controlled, or corrected for, or masked out, a set of an unexpected anomalies of various magnitudes and at various scales have been detected in the current CMB data (Abramo et al 2006;Bernui et al 2007a;Copi et al 2006aCopi et al , 2004Covi et al 2006;Cruz et al 2007;Destri et al 2008;Eriksen et al 2004;Land & Magueijo 2005a) (see also Cabella & Marinucci (2008); Huterer (2006); Martinez-Gonzalez (2008) for recent reviews and references therein). These anomalies call for plausible theoretical explanations since, if robustly detected, these can be used as valuable observables of the physics of the early Universe, or a new window on some of the late time effects (Akofor et al 2007;Bernui & Hipólito-Ricaldi 2008;Brown & Crittenden 2005;Destri et al 2008;Dvorkin et al 2008;Erickcek et al 2008;Inoue & Silk 2007).…”

“…These predictions have been extensively studied in number of works. An incomplete list includes: Abramo et al (2006); Armendariz-Picon & Pekowsky (2008); Bernui et al (2007a,b); Bielewicz et al (2005); Cabella et al (2004Cabella et al ( , 2006Cabella et al ( , 2005; Chen & Szapudi (2006a,b); Chiang et al (2003); Copi et al (2006aCopi et al ( ,b, 2004; Curto et al ( , 2008; de Oliveira-Costa & Tegmark (2006);de Troia et al (2007); Donoghue & Donoghue (2005); Efstathiou (2003); Eriksen et al (2007Eriksen et al ( , 2008Eriksen et al ( , 2004; Gaztañaga et al (2003); ; Hansen et al (2004a,b); Jaffe et al (2005); Komatsu et al (2008); Komatsu et al (2003); Land & Magueijo (2005b; Lew (2008); Lew & Roukema (2008); McEwen et al (2006); Mukherjee & Wang (2004); Naselsky et al (2005Naselsky et al ( , 2007; Park (2004); Park et al (2006); Samal et al (2008); Savage et al (2004); Shandarin (2002); Souradeep et al (2006); Vielva et al (2004); Wiaux et al (2006); Wu et al (2001); Yadav & Wandelt (2008) and references therein. Within the th...…”

Alignment tests for low CMB multipoles

“…Several recent works have reported some anomalies in the data: the low-order multipole values [1,2,4,5,15,18,19,20]; the alignment of some low-order multipoles [6,15,21,22,23]; an unexpected asymmetric distribution on the sky of the large-scale power of CMB data [14,24,25,26,27]; indications for a preferred direction of maximum asymmetry [9,25,27,28,29,30]; as well as apparent non-gaussian features detected via the wavelet method or other analyses [31,32,33,34,35,36]. These anomalies have motivated many explanations, such as compact topologies [37,38], a broken or suppressed spectrum at large scales [39,40,41,42,43,44], oscillations superimposed on the primordial spectrum of density fluctuations [45,46,47], anisotropic cosmological models [48,49,50] and possible extended foregrounds that could be affecting the CMB …”