On Non-Gaussianity in the Cosmic Microwave Background : phenomenology and analysis

Abstract

The goals of this thesis are to provide a general introduction to CMB fundamentals, give an overview of non-Gaussianity analysis, and to compare the sensitivities of a selection of tests (Minkowski functionals, skeleton length and preferred direction $\mathcal{D}$) to two different non-Gaussian element types (galactic foregrounds and a Bianchi type universe model template).

The thesis is divided into three main parts. Part I presents CMB fundamentals and background. In Part II, non-Gaussianities are discussed. Their constitution, significance and sources, and how to test for them, are described. Part III presents the methodology applied, the simulations performed, the analysis conducted, and finally the results obtained.

For the foregrounds, the area and length Minkowski functionals and the skeleton length were of comparable sensitivity. With the skeleton length giving results very similar to the area functional, it does not seem to add value compared to the Minkowski functional set for the data used in these tests. The Minkowski genus was less sensitive, with a detection limit of roughly twice that of the other three.

For a Bianchi type VII$_h$ universe model template the preferred direction $\mathcal{D}$ test was added to the previously mentioned tests. The tests can roughly be divided into two groups. The first, and most sensitive, consists of the Minkowski genus and the preferred direction $\mathcal{D}$. The Minkowski genus was slightly more sensitive than the preferred direction $\mathcal{D}$. The other tests were less sensitive, again roughly by a factor of two, compared to the first group. For this type of non-Gaussianity, the skeleton length gave results very similar to the Minkowski length functional.