dc.contributor.advisor Shellard, Paul dc.contributor.author Lazanu, Andrei dc.date.accessioned 2016-08-08T15:57:04Z dc.date.available 2016-08-08T15:57:04Z dc.date.issued 2016-06-28 dc.identifier.other PhD.39948 dc.identifier.uri https://www.repository.cam.ac.uk/handle/1810/256999 dc.description.abstract Much of the recent progress in cosmology has come from studying the power spectrum of the cosmic microwave background (CMB). The latest results from the Planck satellite confirmed that the inflationary paradigm with the $\Lambda$CDM six-parameter model provides a very good description of the observed structures in the Universe. Even so, additional parameters, such as cosmic defects, are still allowed by current observational data. Additionally, many of the inflationary models predict a significant departure from Gaussianity in the distribution of primordial perturbations. Higher order statistics, such as the bispectrum, are required to test and constrain such models. The late-time distribution of matter in the Universe - large-scale structure (LSS) - contains much more information than the CMB that has not yet been used. In this thesis, we look at both problems: the effects of cosmic defects, in particular cosmic strings and domain walls on the CMB power spectrum through numerical simulations, and the dark matter bispectrum of large-scale structure. Topological defects are predicted by most inflationary theories involving symmetry breaking in the early Universe. In this thesis we study the effects of cosmic strings and domain walls on the CMB by determining their power spectrum. We use Nambu-Goto and field theory simulations for cosmic strings and domain walls respectively, and we determine the power spectra they produce with a modified Einstein-Boltzmann solver sourced by unequal time correlators from components of the energy-momentum tensor of the defects. We use these spectra together with CMB likelihoods to obtain constraints on the energy scales of formation of the cosmic defects, finding $G\mu/c^{2} < 1.29 \times 10^{−7}$ and $\eta < 0.93$ MeV (at 95% confidence level) for cosmic strings and domain walls respectively, when using the Planck satellite likelihoods. For the matter bispectrum of LSS, we compare different perturbative and phenomenological models with measurements from $N$-body simulations by using shape and amplitude correlators and we determine on which scales and for which redshifts they are accurate. We propose a phenomenological ‘three-shape’ model, based on the fundamental shapes we have observed by studying the halo model that are also present in the simulations. When calibrated on the simulations, this model accurately describes the bispectrum on all scales and redshifts considered, providing a prototype bispectrum HALOFIT-like methodology that could be used to describe and test parameter dependencies. en dc.description.sponsorship Science and Technology Facilities Council (STFC), Gonville and Caius College, Cambridge Philosophical Society, Centre for Theoretical Cosmology, Department of Applied Mathematics and Theoretical Physics dc.language.iso en en dc.rights All Rights Reserved en dc.rights.uri https://www.rioxx.net/licenses/all-rights-reserved/ en dc.subject Research Subject Categories::MATHEMATICS::Applied mathematics en dc.subject Research Subject Categories::NATURAL SCIENCES::Physics::Astronomy and astrophysics::Cosmology en dc.subject cosmic microwave background en dc.subject CMB en dc.subject power spectrum en dc.subject cosmic defects en dc.subject dark matter en dc.subject large-scale structure en dc.subject cosmic strings en dc.subject domain walls en dc.subject large-scale structure en dc.subject bispectrum en dc.subject inflation en dc.title The power spectrum and bispectrum of inflation and cosmic defects en dc.type Thesis en dc.type.qualificationlevel Doctoral dc.type.qualificationname Doctor of Philosophy (PhD) dc.publisher.institution University of Cambridge en dc.publisher.department Department of Applied Mathematics and Theoretical Physics en dc.publisher.department Gonville and Caius College en dc.identifier.doi 10.17863/CAM.473
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