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    Cosmological Aspects of Non-Minimal Dark Sectors

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    Author
    Huang, Fei
    Issue Date
    2019
    Keywords
    cosmology
    dark matter
    decay
    free streaming
    strongly coupled
    structure formation
    Advisor
    Dienes, Keith R.
    Su, Shufang
    
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    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction, presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    Many proposals for physics beyond the Standard Model do not give rise to only a single dark-matter candidate --- they give rise to an entire dark sector consisting of many independent dark degrees of freedom. In this dissertation, we explore some of the cosmological implications of such non-minimal dark sectors. In the first part of this dissertation, we examine the phenomenology of dark sectors in which the density of dark states grows exponentially with mass. Ensembles of such states arise naturally as the ``hadronic'' resonances associated with the confining phase of a strongly-coupled dark sector; they also arise naturally as the gauge-neutral bulk states of Type I string theories. We study the dynamical properties of such ensembles, including their effective equations of state, and investigate some of the immediate model-independent observational (astrophysical and cosmological) constraints on such ensembles that follow. Remarkably, we find that these constraints allow such sectors to exhibit energy scales ranging from the GeV scale all the way to the Planck scale, but that the total present-day cosmological abundance of the dark sector must be spread across an increasing number of different states in the ensemble as these energy scales are dialed from the Planck scale down to the GeV scale. In the second part of this dissertation, by contrast, we examine the possibility of non-trivial dynamics within non-minimal dark sectors, focusing on processes in which heavier constituents within a non-minimal dark sector decay to lighter constituents. We begin by demonstrating that such decays can leave non-trivial imprints on the phase-space distribution of the resulting dark matter. Indeed, as a result of these effects, this phase-space distribution need not be thermal --- it can even be multi-modal, with a non-trivial pattern of peaks and troughs as a function of momentum. We then proceed to study how these features can induce non-trivial changes in the shape of the resulting matter power spectrum. The results of this project therefore provide an interesting way of learning about (and potentially even constraining) non-trivial dynamics in the early universe.
    Type
    text
    Electronic Dissertation
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Physics
    Degree Grantor
    University of Arizona
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