This thesis is about cosmological inflation and its relation to observations. In part I we study the observational consequences of an additional scalar field besides the inflaton field. In... Show moreThis thesis is about cosmological inflation and its relation to observations. In part I we study the observational consequences of an additional scalar field besides the inflaton field. In particular, we focus on several different regimes where we vary both the coupling between the fields and the mass of the second field. In part II we perform a statistical analysis to understand whether we can extract some of the traces of new physics present during inflation from the three-dimensional map of galaxies in our universe. Show less
In this work the reconstruction of a tau neutrino signal in the KM3NeT detector is discussed. Tau neutrinos leave a two shower signature in the detector, which is a unique signature among all... Show moreIn this work the reconstruction of a tau neutrino signal in the KM3NeT detector is discussed. Tau neutrinos leave a two shower signature in the detector, which is a unique signature among all neutrino interactions. By identifying and reconstructing these tau signatures the KM3NeT detector will be able to distinguish all three neutrino flavors. In addition, cosmic tau neutrinos suffer significantly less from atmospheric backgrounds, makign them ideal messengers for cosmic events. The presented reconstruction is the first tau reconstruction for the KM3NeT detector and resulted in a total expected observation rate of half a tau event per year for one unit of the KM3NeT detector. Show less
We investigate the buildup of galaxies from various vantage points. The first two chapters focus on the stellar content of galaxies, especially the distribution of stellar masses at birth and... Show moreWe investigate the buildup of galaxies from various vantage points. The first two chapters focus on the stellar content of galaxies, especially the distribution of stellar masses at birth and potential variations therein in various galactic environments. We find that in some cases these inferred variations can be due to an underestimation of model and measurement errors. Furthermore, we infer the consequences of these proposed variations on the interpretation of galaxy properties and galaxy formation processes. Chapters 3 and 4 focus on the buildup of galaxies in time through mergers and in-situ star formation. We test and improve observational models that aim to trace galaxies though cosmic time, by applying them to cosmological hydrodynamical simulations, for which we have access to the full history and evolution of galaxies since the beginning of time. The fifth chapter focusses on the buildup of galaxy morphology. We follow the buildup of morphological components in a cosmological simulation, which leads us to conclude that galaxy formation is a three-phase process, consisting of an early, rather disorganised, phase, followed by a phase in which stars are formed primarily in an organised rotating disk, and ending in a late phase of merger-driven spheroid formation. 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
