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.

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2007 - 200912020 - 20211

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    Cosmological Phase Transition of Composite Higgs Confinement
    (2021) Ekhterachian, Majid; Agashe, Kaustubh; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    We study the cosmological confinement-deconfinement phase transition (PT) of nearly conformal, strongly coupled large N field theories, applicable to composite Higgs models. We find that despite strong coupling, aspects of the PT can be analyzed when the confinement is predominantly spontaneous. In this scenario, the leading contribution to the transition rate can be computed within effective field theory of dilaton-- the pseudo Nambu-Goldstone boson associated with the spontaneous breaking of conformal symmetry. We then show how the holographic dual formulation in terms of 5D warped compactifications allows for qualitative understanding of the missing pieces of the earlier described 4D picture and a quantitative improvement of the calculations. In this description the PT is from a high-temperature black-brane phase to the low-temperature Randall-Sundrum I phase, and the transition proceeds by percolation of bubbles of IR-brane nucleating from the black-brane horizon. We show that the bubble configuration interpolating between the two phases can be smooth enough to be described within 5D effective field theory. We find that cosmological PT in the minimal models can complete only after a large period of supercooling, potentially resulting in excessive dilution of primordial matter abundances. We then show how generic modifications of the minimal models can result in a much faster completion of the PT. We also study the stochastic gravitational wave background produced by the violent bubble dynamics and discuss the implications of the PT for baryogenesis.
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    Submillimeter Test of the Gravitational Inverse-Square Law Using a Superconducting Differential Accelerometer
    (2007-11-21) Prieto, Violeta A; Paik, Ho Jung; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The inverse-square law of gravitation is tested at submillimeter distances. To minimize Newtonian errors, the experiment employs a near null source, a circular disk of large diameter-to-thickness ratio. Two test masses, also disk-shaped, are suspended on the two sides of the source mass at a nominal distance of 180 micrometers. The source mass amplitude of motion is 16.1 micrometers. The signal is detected by a superconducting differential accelerometer. Careful matching and alignment makes the detector highly immune to platform vibrations. To reduce the thermal Brownian motion noise as well as the temperature noise of the instrument, the experiment is cooled to 1.7 K by pumping on liquid helium. In this dissertation, I discuss the assembly, design, and design improvements of the inverse square law experiment. I perform a comprehensive analysis of the errors, identify the problems with the apparatus, and show ways to improve the design of the experiment. With the improved design, it will be possible to achieve a sensitivity of |alpha| = 2 x 10^-3 at lambda = 150 micrometers, which will improve the current experimental limits by one order of magnitude at 150 micrometers and by over two orders of magnitude at shorter distances.