Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

Browse

Filters

2015 - 20202

Settings

Subject: search.filters.subject.Grand Unified Theory

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Cosmological Probes of Physics Beyond the Standard Model
    (2020) Kumar, Soubhik; Sundrum, Raman; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The Standard Model (SM) of particle physics can explain a diverse variety of experimental observations. However, there remain multiple compelling reasons why we believe that the SM is not the final theory of the universe. In this thesis, we first briefly discuss some of those shortcomings of the SM, and then focus on ways in which cosmological observations can be used to probe theories beyond the SM. The primary probe we consider for this purpose is primordial non-Gaussianity (NG) of cosmological perturbations. We show that by precise studies of NG we can probe ultra-high energy gauge theories that might otherwise be energetically completely inaccessible to terrestrial experiments, by focusing first on (i) generic spontaneously broken Higgsed gauge theories, and then on, (ii) higher-dimensional Grand Unified Theories (GUTs). Building upon this, we also discuss a simple curvaton extension of the standard inflationary paradigm where strength of various NG signals can be orders of magnitude larger, and thus be easily accessible via observations in the coming decade.
  • Thumbnail Image
    Item
    Neutrino Mass and Proton Lifetime in a Realistic Supersymmetric SO(10) Model
    (2015) Severson, Matthew Michael; Mohapatra, Rabindra N; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This work presents a complete analysis of fermion fitting and proton decay in a supersymmetric $SO(10)$ model previously suggested by Dutta, Mimura, and Mohapatra. A key question in any grand unified theory is whether it satisfies the stringent experimental lower limits on the partial lifetimes of the proton. In more generic models, substantial fine-tuning is required among GUT-scale parameters to satisfy the limits. In the proposed model, the {\bf 10}, $\overline{\bf{126}}$, and {\bf 120} Yukawa couplings contributing to fermion masses have restricted textures intended to give favorable results for proton lifetime, while still giving rise to a realistic fermion sector, without the need for fine-tuning, even for large $\tan\beta$, and for either type-I or type-II dominance in the neutrino mass matrix. In this thesis, I investigate the above hypothesis at a strict numerical level of scrutiny; I obtain a valid fit for the entire fermion sector for both types of seesaw dominance, including $\theta_{13}$ in good agreement with the most recent data. For the case with type-II seesaw, I find that, using the Yukawa couplings fixed by the successful fermion sector fit, proton partial lifetime limits are readily satisfied for all but one of the pertinent decay modes for nearly arbitrary values of the triplet-Higgs mixing parameters, with the $K^+ \bar\nu$ mode requiring a minor ${\cal O}(10^{-1})$ cancellation in order to satisfy its limit. I also find a maximum partial lifetime for that mode of $\tau(K^+ \bar\nu) \sim 10^{36}$\,years. For the type-I seesaw case, I find that $K^+ \bar\nu$ decay mode is satisfied for any values of the triplet mixing parameters giving no major enhancement, and all other modes are easily satisfied for arbitrary mixing values; I also find a maximum partial lifetime for $K^+ \bar\nu$ of nearly $10^{38}$\,years, which is largely sub-dominant to gauge boson decay channels.