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Exploring the universe with cosmic microwave background non-Gaussianity

Final Activity Report Summary - CMB-NONGA-NOR (Exploring the universe with cosmic microwave background non-Gaussianity)

According to modern cosmology, the universe underwent a phase of extremely rapid expansion during the first fractions of a second after the Big Bang. This period of rapid expansion is known as inflation. During the inflationary period, potential energy in the vacuum was converted into matter and radiation energy. The universe was filled with hot, ionized gas as well as energetic electromagnetic radiation. As the universe expanded, the gas cooled and about half a million years after the Big Bang, the temperature of the gas was such that the first atoms in the universe could form. This period is called the recombination period. Before recombination, the electromagnetic radiation was continuously scattered on charged particles. The universe is said to become transparent at recombination as the radiation from that time was allowed to stream freely without the continuous scattering process. This radiation can still be observed today and is called the Cosmic Background Radiation (CMB). By mapping the temperature of this radiation in different directions on the sky one can create a picture of the universe as it appeared at the recombination epoch. The physics of the primordial universe is much easier studied by analysing this snapshot of the universe in a very early epoch.

In this project, we have studied the statistical distribution of the temperature fluctuations of the CMB. The theory of inflation which has been highly successful in explaining several properties of the current universe makes very few testable predictions. Only two robust predictions of inflation are known: the existence of a background of so-called gravitational waves and a slightly non-Gaussian distribution of the CMB temperature fluctuations. Gravitational waves are technologically very hard to detect and inflationary gravitational waves are not expected to be detected within the next 10-20 years. However, the European Planck Satellite scheduled for launch in 2008 will have the capability to study the statistical distribution of the CMB to high precision. In this project, we have made predictions for the Planck Satellite and the level of non-Gaussianity which can be seen by this Satellite. By using supercomputers, we have been able to simulate observations that the Planck Satellite would make in a universe with different models of inflation.

By analysing these simulations we have shown that there is a fair chance that this non-Gaussianity will be detected by the Planck Satellite if the inflationary theory does indeed correctly describe the physical processes in the universe during its first fractions of a second. Further analysis is necessary in order to accurately quantify the level to which these non-Gaussianities can be seen.