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The impact of weakly coupled fields on the accelerated expansion and its observables / by Jannis Bielefeld

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Author	Bielefeld, Jannis
Title	The impact of weakly coupled fields on the accelerated expansion and its observables / by Jannis Bielefeld
Date	2015
Abstract	The accelerated expansion of space in the Universe has been known for two decades. However, finding a plausible theory that describes this expansion is more difficult: Taking general relativity for granted requires us to stipulate the existence of a new component that makes up 70 percent of the Universes total energy budget. The negative pressure of this dark energy causes the Universe to expand at an accelerated rate. The simplest model, the cosmological constant, suffers from a crucial problem: the numerical value has to be finely tuned 120 orders of magnitude smaller than the scales where we would expect it to be. Moreover, from a model-building point of view the way this vacuum energy appears in the theory is less than satisfactory. More realistic models invoke cosmological scalar fields that dynamically resemble the cosmological constant at late times. These have nicer properties. Two properties of these we can measure are its abundance and the ratio of energy and pressure densities. That is already enough to constrain the model configuration space considerably. However, the properties of this dark fluid are still unconstrained by the data during the early phases of the Universe and many possible scenarios are open to speculation as long as they do not affect the geometry of the Universe too much. Generally this is achieved by assuming a vanishing dark energy density early on. This does not have to be the case, though. The dark fluid can resemble other components of the Universe before transitioning to dark energy and mimic their behavior. Moreover, it can have more complicated effects than what can be modeled by simple scalar fields { gauge fields lead the way here. Their effect on some components of the Universe, gravitational waves in this case, is heavily non-standard. In this thesis we calculate the efects that different kinds of dark fluids have on the cosmological observables. Particular emphasis is on early dark fluids { dark energy or dark radiation { and their effect on the cosmological evolution. We constrain the validity of these theories and discuss effects that still have to be confirmed by future surveys.
Description	1 online resource (xvii, 175 leaves) : illustrations (some color)
Format	application/pdf
College	Dartmouth College -- Department of Physics and Astronomy.
Issuing Body	Dartmouth Dissertations are made available through the Dartmouth Digital Library.
Degree	Thesis (Ph.D.)--Dartmouth College.
Copyright	All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means without permission in writing from the author.
DOI	http://dx.doi.org/10.1349/ddlp.1601

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