ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
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Description
In this thesis a new method based on the Tight-Binding Linear Muffin Tin Orbital (TB-LMTO) formalism and the Quasiparticle Self-consistent GW (QSGW) approximation is proposed. The method is capable of generating accurate electronic bands structure of large supercells necessary to model alloys structures. The strategy consist in building simple and small hamiltonian from linear Muffin-tin-orbitals (LMTO). Parameters in this hamiltonian are then used to fit the difference in QSGW self-energies and LDA exchange-correlation potentials. The parameter are assumed to transfer to new environments --- a procedure we check carefully by comparing our predicted band to QSGW bands for small supercells. The method possess both the accuracy of the QSGW approximation, (which is the most reliable way to determine energy bands accurately, and yet too expensive for the large supercells required here), and the efficiency of the TB-LMTO method. The accurate and highly efficient hamiltonian is used to predict the electronic and optical transitions of Si1-xGex alloys and SnxSiyGe1-x-y alloys. The goal is to engineer direct band gap material compatible with the silicon technology. The results obtained are compared to available experimental data.
ContributorsDonfack, Hermann Azemtsa (Author) / Van Schilfgaarde, Mark (Thesis advisor) / Dow, John D. (Thesis advisor) / Ponce, Fernando (Committee member) / Ritchie, Barry (Committee member) / Chamberlin, Ralph (Committee member) / Arizona State University (Publisher)
Created2011
Description
In this thesis, applications of sparsity, specifically sparse-tensors are motivated in physics.An algorithm is introduced to natively compute sparse-tensor's partial-traces, along with direct implementations in popular python libraries for immediate use. These applications include the infamous exponentially-scaling (with system size) Quantum-Many-Body problems (both Heisenberg/spin-chain-like and Chemical Hamiltonian models). This sparsity aspect is stressed as an important and essential feature in solving many real-world physical problems approximately-and-numerically. These include the original motivation of solving radiation-damage questions for ultrafast light and electron sources.
ContributorsCandanedo, Julio (Author) / Beckstein, Oliver (Thesis advisor) / Arenz, Christian (Thesis advisor) / Keeler, Cynthia (Committee member) / Erten, Onur (Committee member) / Arizona State University (Publisher)
Created2023
Description
In this dissertation two kinds of strongly interacting fermionic systems were studied: cold atomic gases and nucleon systems. In the first part I report T=0 diffusion Monte Carlo results for the ground-state and vortex excitation of unpolarized spin-1/2 fermions in a two-dimensional disk. I investigate how vortex core structure properties behave over the BEC-BCS crossover. The vortex excitation energy, density profiles, and vortex core properties related to the current are calculated. A density suppression at the vortex core on the BCS side of the crossover and a depleted core on the BEC limit is found. Size-effect dependencies in the disk geometry were carefully studied. In the second part of this dissertation I turn my attention to a very interesting problem in nuclear physics. In most simulations of nonrelativistic nuclear systems, the wave functions are found by solving the many-body Schrödinger equations, and they describe the quantum-mechanical amplitudes of the nucleonic degrees of freedom. In those simulations the pionic contributions are encoded in nuclear potentials and electroweak currents, and they determine the low-momentum behavior. By contrast, in this work I present a novel quantum Monte Carlo formalism in which both relativistic pions and nonrelativistic nucleons are explicitly included in the quantum-mechanical states of the system. I report the renormalization of the nucleon mass as a function of the momentum cutoff, an Euclidean time density correlation function that deals with the short-time nucleon diffusion, and the pion cloud density and momentum distributions. In the two nucleon sector the interaction of two static nucleons at large distances reduces to the one-pion exchange potential, and I fit the low-energy constants of the contact interactions to reproduce the binding energy of the deuteron and two neutrons in finite volumes. I conclude by showing that the method can be readily applied to light-nuclei.
ContributorsMadeira, Lucas (Author) / Schmidt, Kevin E (Thesis advisor) / Alarcon, Ricardo (Committee member) / Beckstein, Oliver (Committee member) / Erten, Onur (Committee member) / Arizona State University (Publisher)
Created2018
Description
The OLYMPUS experiment measured the two-photon exchange contribution to elastic electron-proton scattering, over a range of four-momentum transfer from \(0.6 < Q^2 < 2.2\) \((\mathrm{GeV/c})^2\). The motivation for the experiment stemmed from measurements of the electric-to-magnetic form factor ratio of the proton \(\mu G_E/G_M\) extracted from polarization observables in polarized electron-proton scattering. Polarized electron-proton scattering experiments have revealed a significant decrease in \(\mu G_E/G_M\) at large \(Q^2\), in contrast to previous measurements from unpolarized electron-proton scattering. The commonly accepted hypothesis is that the discrepancy in the form factor ratio is due to neglected higher-order terms in the elastic electron-proton scattering cross section, in particular the two-photon exchange amplitude.
The goal of OLYMPUS was to measure the two-photon exchange contribution by measuring the positron-proton to electron-proton elastic scattering cross section ratio, \(\sigma_{e^+p}/\sigma_{e^-p}\). The two-photon exchange contribution is correlated to the deviation of the cross section ratio from unity.
In 2012, the OLYMPUS experiment collected over 4 fb\(^{-1}\) of \(e^+p\) and \(e^-p\) scattering data using electron and positron beams incident on a hydrogen gas target. The scattered leptons and protons were measured exclusively with a large acceptance spectrometer. OLYMPUS observed a slight rise in \(\sigma_{e^+p}/\sigma_{e^-p}\) of at most 1-2\% over a \(Q^2\) range of \(0.6 < Q^2 < 2.2\) \((\mathrm{GeV/c})^2\). This work discusses the motivations, experiment, analysis method, and the preliminary results for the cross section ratio as measured by OLYMPUS.
The goal of OLYMPUS was to measure the two-photon exchange contribution by measuring the positron-proton to electron-proton elastic scattering cross section ratio, \(\sigma_{e^+p}/\sigma_{e^-p}\). The two-photon exchange contribution is correlated to the deviation of the cross section ratio from unity.
In 2012, the OLYMPUS experiment collected over 4 fb\(^{-1}\) of \(e^+p\) and \(e^-p\) scattering data using electron and positron beams incident on a hydrogen gas target. The scattered leptons and protons were measured exclusively with a large acceptance spectrometer. OLYMPUS observed a slight rise in \(\sigma_{e^+p}/\sigma_{e^-p}\) of at most 1-2\% over a \(Q^2\) range of \(0.6 < Q^2 < 2.2\) \((\mathrm{GeV/c})^2\). This work discusses the motivations, experiment, analysis method, and the preliminary results for the cross section ratio as measured by OLYMPUS.
ContributorsIce, Lauren (Author) / Alarcon, Ricardo O (Thesis advisor) / Dugger, Michael (Committee member) / Lebed, Richard (Committee member) / Ritchie, Barry (Committee member) / Arizona State University (Publisher)
Created2016
Description
The GlueX experiment housed in Hall D of the Thomas Jefferson National Laboratory was created to map the light meson spectrum in order to contribute to the Standard Model of particle physics by strengthening our understanding of the strong interaction. GlueX is a medium-energy photoproduction experiment that utilizes a linearly polarized photon beam to create hadronic forms of matter. By mapping the light meson spectrum, the GlueX collaboration hopes to identify meson states forbidden by the Constituent Quark Model. As a main research objective, the GlueX collaboration is searching for hybrid $q\bar{q}g$ meson states that exhibit exotic quantum numbers. One hybrid meson candidate is the $\eta'_1$, which is predicted to decay to $K^\ast\bar{K}$ and have a mass near $2.3~\mathrm{GeV}$ (\citeauthor{qn_exotic_status}, \citeyear{qn_exotic_status}; \citeauthor{hybrid_mesons}, \citeyear{hybrid_mesons}). At this time, very few meson states have been identified in the $2.0~\mathrm{GeV}$ mass region. This dearth of evidence for existing states requires any tool developed to search for meson states above $2.0~\mathrm{GeV}$ must be verified by looking at known meson states. In order to search for the $\eta'_1$ hybrid meson candidate in $\gamma p \rightarrow pK^+K^-\gamma\gamma$ events, meson states decaying $K^\ast\bar{K}$ that contribute to the low mass region must be identified, defined in this document as particles having masses between $1400$ and $1600~\mathrm{MeV}$. Identifying what meson states exist in the low mass region is also critical to mapping the light meson spectrum and determining the quark-gluonic content of those meson states. The results of a partial wave analysis (PWA) of $\gamma p \rightarrow pX$ where $X\rightarrow K^\ast\bar{K}$ from $\gamma p \rightarrow pK^+K^-\gamma\gamma$ events in GlueX are presented. In the $J=0$ invariant mass distribution, the $\eta(1405)$ and $\eta(1475)$ are identified, adding to the debate as to whether two pseudoscalar mesons exist in the low mass region. For the $J=1$ distribution, the $f_1(1420)$ and $f_1(1510)$ axial vector mesons are seen, where the former helps further elaborate on the $E\iota$ puzzle of the twentieth century \citep{E_iota_puzzle}. With respect to the controversy of meson states in the low mass region, evidence for the existence of the $f_2(1430)$ meson is strengthened in the $J=2$ distribution, and the $f'_2(1525)$ state is seen. This work lays a foundation for the ASU Meson Physics Group to continue a wider search for hybrid mesons in the $\gamma p \rightarrow pK^+K^-\gamma\gamma$ reaction topology.
ContributorsCole, Sebastian Miles (Author) / Dugger, Michael (Thesis advisor) / Ritchie, Barry (Committee member) / Alarcon, Ricardo (Committee member) / Shovkovy, Igor (Committee member) / Arizona State University (Publisher)
Created2021