It is an established fact that the Standard Model has to be extended to explain the so-called Beyond the Standard Model (BSM) phenomena: dark matter, matter-antimatter asymmetry of the Universe and... Show moreIt is an established fact that the Standard Model has to be extended to explain the so-called Beyond the Standard Model (BSM) phenomena: dark matter, matter-antimatter asymmetry of the Universe and neutrino flavour oscillations. The difficulty of direct detection of new particles lies in the huge parameter space of the possible candidates. Hence, data coming from the cosmological and astrophysical observations provide invaluable directions for laboratory experiments.In this thesis we explore two methods of constraining new-physics candidates: through their influence on the primordial nucleosynthesis and through observable differences in the matter distribution caused by free-streaming of the dark-matter particles. We concentrate on the well-motivated extension of the SM that aims at explaining all 3 BSM problems at the same time: the Neutrino Minimal Standard Model. In this extension, there are 3 additional heavy neutral leptons, one of which plays the role of dark matter, while the other two are necessary for induction of matter-antimatter asymmetry and neutrino oscillations. The dark-matter candidate is an example of a Warm Dark Matter particle, the free-streaming of which might be detected in the Lyman-α forest spectra of distant quasars. The other two particles have lifetimes that make them relevant to the primordial nucleosynthesis. Show less
The nature of the Dark Matter is one of the biggest open questions in modern cosmology and particle physics. The work in this thesis concerns a search for the observational effects of one... Show moreThe nature of the Dark Matter is one of the biggest open questions in modern cosmology and particle physics. The work in this thesis concerns a search for the observational effects of one particular class of hypothetical Dark Matter particles, namely those that are allowed to decay. In decaying, X-ray photons are emitted and should be observable. One part of the thesis details the discovery of a potential Dark Matter decay signal in X-ray spectra of galaxies and galaxy clusters, and the subsequent efforts to identify its origin. To this end archival data and new observations are compared to the respective Dark Matter masses of the observed objects. Interpretations of the signal as an instrumental effect, or due to regular astrophysical processes are unsatisfactory. Although the Dark Matter interpretation remains plausible, definitive conclusions about the origin of the signal can not be drawn yet and will require measurements by next generation observatories. The last chapter of the thesis contains the proof-of-concept of a novel technique to search for such weak signals that combines increased statistical power with the ability to determine the physical origin of a signal, while avoiding some of the disadvantages of traditional methods. Show less
A microscopic origin of dark matter phenomenon is the most plausible hypothesis to explain the mystery of dark matter. The dark matter particle hypothesis necessarily implies an extension of the... Show moreA microscopic origin of dark matter phenomenon is the most plausible hypothesis to explain the mystery of dark matter. The dark matter particle hypothesis necessarily implies an extension of the Standard Model. In this thesis, we undertook a systematic model-independent program of studying the properties of decaying dark matter. By analyzing the experimental data for dwarf spheroidal galaxies it was shown that the X-ray energy range is a preferred region when searching for radiatively decaying dark matter. By analyzing dark matter distributions in different types of galaxies and in galaxy clusters we show that the expected dark matter signal increases slowly with the mass of the object. Therefore, dwarf and spiral galaxies are the observational targets with the optimal signal-to-noise ratio. To probe the theoretically interesting regions of particle physics models we performed a combined analysis of a very large dataset of archival XMM-Newton observations of galaxies. Finally, we discussed an ultimate way to probe the whole parameter space of minimal models of decaying dark matter. We argue that a new X-ray telescope with the narrow energy resolution (comparable to internal width of the line) and large field-of-view is required. Show less
