Statistical Tests for the Gaussian Nature of Primordial Fluctuations Through CBR Experiments

Abstract

Information about the physical processes that generate the primordial fluctuations in the early universe can be gained by testing the Gaussian nature of the fluctuations through cosmic microwave background radiation (CBR) temperature anisotropy experiments. One of the crucial aspects of density perturbations that are produced by the standard inflation scenario is that they are Gaussian, whereas seeds produced by topological defects left over from an early cosmic phase transition tend to be non-Gaussian. To carry out this test, sophisticated statistical tools are required. In this paper, we will discuss several such statistical tools, including multivariant skewness and kurtosis, Euler-Poincare characteristics, the three point temperature correlation function, and the Hotelling's $T^2$ statistic defined through bispectral estimates of a one dimensional dataset. The effect of noise present in the current data is discussed in detail and the COBE 53 GHz dataset is analyzed. Our analysis shows that, on the large angular scale to which COBE is sensitive, the statistics are probably Gaussian. On the small angular scales, the importance of Hotelling's $T^2$ statistic is stressed, and the minimum sample size required to test Gaussianity is estimated. Although the current dataset available from various experiments at half-degree scales is still too small, improvement of the dataset by roughly a factor of two will be enough to test the Gaussianity statistically. On the arcminute scales, we analyze the recent RING data through bispectral analysis, and the result

44 pages, Latex (15 Figures not included)

References in corpus (6)

• Dipole Anisotropy in the COBE DMR First-Year Sky Maps
• The Angular Dependence of the Three-Point Correlation Function of the Cosmic Microwave Background Radiation as Predicted by Inflationary Cosmologies
• Testing for Gaussianity Through the Three Point Temperature Correlation Function
• On the Statistics of CMB Fluctuations Induced by Topological Defects
• Cosmic Variance in CMB Anisotropies: From $1^{\circ }$ to COBE
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• On the Non-Gaussianity Observed in the COBE-DMR Sky Maps
• Is the cosmic microwave background really non-Gaussian?
• Estimate of the Cosmological Bispectrum from the MAXIMA-1 Cosmic Microwave Background Map
• On the trispectrum as a gaussian test for cosmology
• Multiple Methods for Estimating the Bispectrum of the Cosmic Microwave Background with Application to the MAXIMA Data
• The correlation of peaks in the microwave background
• Statistical Power, the Bispectrum and the Search for Non-Gaussianity in the CMB Anisotropy
• Non-Gaussianity: Comparing wavelet and Fourier based methods
• Multi-variate joint PDF for non-Gaussianities: exact formulation and generic approximations
• A new statistic for picking out Non-Gaussianity in the CMB
• Cosmic confusion
• Searching for Long Strings in CMB Maps