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We present cosmological parameter constraints obtained from galaxy clusters identified by their SunyaevZel'dovich effect signature in the 2500 square-degree South Pole Telescope Sunyaev Zel'dovich (SPT-SZ) survey. We consider the 377 cluster candidates identified at z > 0.25 with a detection significance greater than five, corresponding to the 95% purity threshold for the survey. We compute constraints on cosmological models using the measured cluster abundance as a function of mass and redshift. We include additional constraints from multi-wavelength observations, including Chandra X-ray data for 82 clusters and a weak lensing-based prior on the normalization of the mass-observable scaling relations. Assuming a spatially flat Lambda CDM cosmology, we combine the cluster data with a prior on H-0 and find sigma(8)= 0.784. +/- 0.039 and Omega(m) = 0.289. +/- 0.042, with the parameter combination sigma(8) (Omega(m)/0.27)(0.3) = 0.797 +/- 0.031. These results are in good agreement with constraints from the cosmic microwave background (CMB) from SPT, WMAP, and Planck, as well as with constraints from other cluster data sets. We also consider several extensions to Lambda CDM, including models in which the equation of state of dark energy w, the species-summed neutrino mass, and/or the effective number of relativistic species (N-eff) are free parameters. When combined with constraints from the Planck CMB, H-0, baryon acoustic oscillation, and SNe, adding the SPT cluster data improves the w constraint by 14%, to w = -1.023 +/- 0.042.

Cosmology, as an all-encompassing theoretical construction of universal reality, serves as one of the best indicators for a variety of philosophical, scientific, and cultural values. Within any cosmological system, the question of extraterrestrial life is an important element. Mere existence or nonexistence, however, only exposes a small portion of the ideological significance behind the contemplation of life outside of earth. The manners by which both believers and disbelievers justify their opinions and the ways they characterize other worlds and their inhabitants show much more about the particular ideas behind such decisions and the general climate of thought surrounding those who consider the topic. By exploring both physical and abstract structures of the universe, and specifically concepts on the plurality of worlds and extraterrestrial life, Western European thought in the seventeenth and eighteenth centuries reveals not an era of pure advancement and modernization, but as a time of both tradition and change.

This thesis presents the spectroscopic observations of the Supernova Legacy Survey (SNLS) from the Gemini-North telescope from May 2006 – May 2008. During this time 68 of 95 targets were confirmed as Type Ia supernovae (SNe Ia) or classified as probable SNe Ia events. We use these objects and reanalyse other high-z spectra obtained as part of SNLS to search for signs of evolution in SNe Ia properties. To do this we use a multicolour method to remove host galaxy contamination from the high-z spectra and measure the equivalent widths of three spectral features in the rest-frame blue part of the spectrum: CaII H&K, SiII and Mg II. These are compared to a sample of low-z objects drawn from the literature. No evidence for evolution is found, but a change in the properties of the SiII feature is observed. This can be explained by changing supernova demographics, an outcome of the two-component progenitor model for SNe Ia. The utility of SNe Ia supernovae for cosmology is confirmed and the possible use of spectral features as alternative calibrators is investigated. The equivalenth width of the SiII feature is anticorrelated with light curve stretch and this is used to define a "spectral stretch" from the low-z sample, which is used to reduce the scatter in the low-z sample. This holds promise for improving the calibration of high-z SNe Ia, particularly if new facilities are used to provide higher-quality spectra.

The observed constraints on the variability of the proton to electron mass ratio and the fine structure constant are used to establish constraints on the variability of the Quantum Chromodynamic Scale and a combination of the Higgs Vacuum Expectation Value and the Yukawa couplings. Further model dependent assumptions provide constraints on the Higgs VEV and the Yukawa couplings separately. A primary conclusion is that limits on the variability of dimensionless fundamental constants such as and provide important constraints on the parameter space of new physics and cosmologies.

It is likely that the early Universe was pervaded by a whole host of scalar fields which are ubiquitous in particle physics models and are employed everywhere from driving periods of accelerated expansion to the spontaneous breaking of gauge symmetries. Just as these scalar fields are important from a particle physics point of view, they can also have serious implications for the evolution of the Universe. In particular in extreme cases their dynamical evolution can lead to the failure of the synthesis of light elements or to exceed the dark matter bound in contrast to observation. These scalar fields are not however isolated systems and interact with the degrees of freedom which comprise their environment. As such two interrelated effects may arise; fluctuations and dissipation. These effects, which are enhanced at finite temperature, give rise to energy transfer between the scalar field and its environment and as such should be taken into account for a complete description of their dynamical evolution. In this thesis we will look at these effects within the inflationary era in a scenario termed warm inflation where amongst other effects, thermal fluctuations can now act as a source of primordial density perturbations. In particular we will show how a model of warm inflation based on a simple quartic potential can be brought back into agreement with Planck data through renormalizable interactions, whilst it is strongly disfavoured in the absence of such effects. Moving beyond inflation, we will consider the effect of fluctuation-dissipation dynamics on other cosmological scalar fields, deriving dissipation coefficients within common particle physics models. We also investigate how dissipation can affect cosmological phase transitions, potentially leading to late time periods of accelerated expansion, as well as presenting a novel model of dissipative leptogenesis.

Dwarf galaxies are powerful tools in the study of galactic evolution. As the most numerous galaxies in the universe, they probe a diverse range of environments: some exist in near-isolation, allowing us to study how a galaxy’s evolution depends on its intrinsic properties. Others have been accreted by larger galaxies and show the impact of environmental processes such as tidal stripping. Because dwarf galaxies have shallow potential wells, these processes leave strong signatures in their star formation histories (SFHs). We use state-of-the-art cosmological hydrodynamical simulations to study the evolution of dwarf galaxies in Local Group analogues. Their SFHs are remarkably diverse, but also show robust average trends with stellar mass and environment. Low- mass isolated dwarfs (10^5 < M∗/M⊙ < 10^6) form all of their stars in the first few Gyr, whereas their more massive counterparts have extended star formation histories, with many of the most massive dwarfs (10^7 < M∗/M⊙ < 10^9) continuing star formation until the present day. Satellite dwarfs exhibit similar trends at early and intermediate times, but with substantially suppressed star formation in the last ∼ 5 Gyr, likely as a result of gas loss due to tidal and ram-pressure stripping after entering the haloes of their primaries. These simple mass and environmental trends are in good agreement with the derived SFHs of Local Group dwarfs whose photometry reaches the oldest main sequence turnoff. SFHs of galaxies with less deep data show deviations from these trends, but this may be explained, at least in part, by the large galaxy-to-galaxy scatter, the limited sample size, and the large uncertainties of the inferred SFHs. / Graduate

Solid inflation is a unique inflationary model, in which inflatons have time-independent but spatially dependent vacuum expectation values. Since it does not conform to conventional inflationary models, it gives quite unique observational predictions, which in principle can be tested by observations. However, the original version of solid inflation hypothesizes an ideal type of solid: an isotropic solid. As a generalization, this thesis discusses a more realistic solid, which has a symmetry under a point group. As a result, its underlying structure can be maximally anisotropic even though it can still give isotropic predictions at the background and quadratic fluctuations in scalar modes. In another branch of generalizations, this thesis performs a thorough analysis of higher-derivative interactions in solid inflation, which the original version ignores.

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