Dark Matter Contribution to the Isotropic Extragalactic Gamma-Ray Background
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- Institutt for fysikk 
This thesis looks into the possibilities of finding a signal from dark matter annihilation in the isotropic extragalactic gamma-ray background radiation (EGBR), and compares the the results with data from the Fermi Large Array Telescope (FLAT). The dark matter candidate in question is the lightest supersymmetric particle (LSP), which is one of the most well motivated candidates. Investigating the possibilities of finding such a signal, can help put constraints on the existing theories of the LSP mass and how dark matter is distributed in the Universe. Also, it can shed a light on what one can do in the future to put even further constraints on existing models. One of the problems, which is not discussed here, is creating good models of other processes can also contribute to the isotropic EGBR, and how these can affect the search for an indirect signal. In order to investigate such a signal in the EGBR, three possible masses of the dark matter candidate, and three possible models of dark matter distribution are looked into, and two possible annihilation channels which have photons as their observable end products are studied - partons hadronising into neutral pions which then decay, and electron-positron pairs. The gamma-ray flux after propagation through the Universe is calculated and then compared with the measured flux by the FLAT. One finds that some models can be excluded, while others can explain some of the observed isotropic EGBR, but not all. This means that one have to find other means to eventually detect dark matter signals, or better models for all contributions to the EGBR must be developed. For the highest mass considered, the data from the FLAT has not yet extended to the energy ranges required, so this is an area where future research must look into, unless high dark matter candidate masses can be excluded by other means.