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Title: Cosmological consequences of coupled quintessence
Author: Noble Chamings, Finlay H.
ISNI:       0000 0004 8506 5582
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2019
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Understanding the cause of the observed accelerating expansion of the universe is one of the most pressing problems in cosmology. To this end, I investigate two classes of dark energy models and their cosmological implications. These comprise growing neutrino quintessence, in which dark energy is coupled to the neutrinos, and models in which dark energy interacts with dark matter via a pure momentum coupling. The standard model of cosmology, LambdaCDM, is introduced, along with the issues it faces that motivate the study of alternatives. I also describe the various sources of cosmological data which provide the basis for stringent tests to be carried out on cosmological models. Following this I discuss a class of alternatives to LambdaCDM known as dynamical dark energy, with a focus on quintessence and interacting dark energy. Having discussed the necessary motivation and background, I proceed to present a study of growing neutrino quintessence cosmologies. Working at the level of the background equations of motion in the Einstein frame I carry out an analytic calculation finding important disagreement with previous results. Numerical evolution of the same equations yields constraints on growing neutrino quintessence cosmologies from the lack of observation of early dark energy in the Planck Collaboration analysis of cosmic microwave background data. I also perturb the equations of motion to linear order in a frame in which the strength of gravity and the particle masses depend on the dark energy field, with a view to gaining a more detailed understanding of the model behaviour. The focus then turns to models in which dark energy interacts with dark matter via a pure momentum coupling. I review previous work which has found such models to be capable of easing tensions between early and late probes of structure formation and present an analytic argument as to why this behaviour occurs. I broaden the analysis by considering a range of coupling functions and potentials, finding that structure growth suppression is present for rather generic choices. In particular, a steeper potential can increase the suppression, without giving rise to an unrealistically small present-day expansion rate provided the coupling parameter is sufficiently large. Both models prove promising in addressing some of the outstanding issues with our current understanding of cosmology, and the present analysis provides improved prospects for constraining or detecting these types of dark energy in future studies.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QB Astronomy