In this thesis we study the use of Boltzmann codes for simulating the evolution of linear perturbations. More specifically we compared the matter power spectra at present as calculated by CAMB and...Show moreIn this thesis we study the use of Boltzmann codes for simulating the evolution of linear perturbations. More specifically we compared the matter power spectra at present as calculated by CAMB and CLASS, as these are the most up to date Boltzmann codes. We have looked at their behavior for a universe with a non-cold dark matter component. For the non-cold dark matter component we used sterile neutrinos with few keV mass and a non thermal primordial distribution function. There is a strong disagreement between the two codes, when the non thermal component is big. We expect a suppression of the matter power spectrum on small scales when comparing it to the cold dark matter case. While CAMB fits our expectations, we see a big deviation in the results from CLASS. An attempt at solving this error was made by changing the way the distribution function is sampled in CLASS however, we only found a small improvement and no conclusive source of this strange behavior.Show less
