Higgs-Portal and Z'-Portal Dark Matters in Brane-World Cosmologies

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University of Alabama Libraries

According to various astrophysical and cosmological observations, Dark Matter (DM) accounts for approximately 27% of the Universe's total energy density. However, no viable DM particle candidate exists within the framework of the Standard Model (SM) of particle physics. An electrically neutral, weakly interacting massive particle (WIMP) from physics beyond theSM emerges as an appealing candidate for DM. In this dissertation research, we consider the WIMP DM model within the framework of 5-dimensional brane-world cosmology. In this setup, our familiar 3-dimensional space is realized as a hyper-surface embedded in a 4-dimensional space. Within this context, all SM and DM fields are confined to the hyper-surface, while the graviton resides in the bulk. We explore two well-established brane-world cosmologies: the Randall-Sundrum (RS) and the Gauss-Bonnet (GB)brane-world cosmologies. These models reproduce the standard Big Bang cosmology at temperatures below the so-called "transition temperature." However, at higher temperatures, they introduce significant modifications to the universe's expansion dynamics. This non-standard expansion law directly influences the predictions related to WIMP DM physics.In our investigation, we consider two well-founded WIMP DM models: the Higgs-portal scalar DM model and the Z′-portal DM model. We analyze the effects of brane-world cosmology and identify the allowed parameter space by incorporating constraints from the observed DM relic density, as well as data from direct and indirect DM detection experiments. It is worth noting that for both DM models, the allowed parameter regions are severely restricted within the conventional Big Bang cosmological framework. Our findings reveal that these allowed parameter regions face even more stringent limitations in the RS cosmology, and in some cases, they may even disappear entirely. Conversely, the GB cosmological effects significantly expand the regions of parameter space that are allowed. Furthermore, the discovery of Higgs-portal or Z′-portal DM within the GB brane-worldcosmology would enable us to determine the transition temperature.

Electronic Thesis or Dissertation
Brane-world, Dark Matter, Higgs-portal, Higher dimensional cosmology, Z'-portal