Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005. / Includes bibliographical references (p. 167-173). / In this thesis we study four-dimensional supersymmetric gauge theories and their string theory realization. After an introduction and a brief review of some basic concepts at the interface of gauge theories and string theory, we begin by examining the duality cascade phenomenon for quiver gauge theories. We give a general formulation for these cascades and use it to identify an example of a duality wall in a theory which can be realized on D3-branes at the apex of the complex cone over the zeroth Hirzebruch surface with the addition of fractional branes. Next, we compute global U(1) charges for the matter fields of the del Pezzo gauge theories and formulate several of their features in the language of exceptional Lie algebras. We suggest the possibility of global symmetry enhancement at infinite coupling for these theories. Finally, we present two contributions to the solution of the geometric engineering problem. We construct the toric phases of the yp,q theories and then identify and study a new infinite family of quiver gauge theories, Xpq, whose dual geometries are known in terms of toric diagrams. / by Pavlos Kazakopoulos. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2009. / In title on title page, "[delta] appear as upper case Greek letter. Cataloged from PDF version of thesis. / Includes bibliographical references (p. 161-165). / This work studies two double polarized pion electroproduction reactions 1(e', e'p)o0 and H(e', e'r+)n near the A region at the MIT-Bates Linear Accelerator Center. With the Bates Large Acceptance Spectrometer Toroid (BLAST) detector package, data were collected simultaneously for both reaction channels, covering an invariant mass range of 1.1 to 1.4 GeV and a squared four momentum transfer range of 0.1 to 0.4 (GeV/c)2. By flipping the target spin direction and the electron beam helicity, the single- (beam only and target only) and double-spin (beam-target) asymmetries were constructed from the measured yields with different spin combinations, covering two kinematic setups: longitudinal and transverse target spin orientations (with respect to the three momentum transfer direction). With a non-zero target spin angle (with respect to the beam direction), this experiment reports for the first time the full angular dependence of asymmetries, compared with theoretical predictions by several pion production models. In some kinematic bins, signs of preference of data to a specific model have been seen, and hints of systematic deviation of data from models have also been observed. Thus, the necessity of new constraints to the pion production models is indicated by this work. / by Yuan Xiao. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1999. / Includes bibliographical references (p. 205-212). / by Kent R. Thurber. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1996. / Includes bibliographical references (leaves 173-186). / by Nathan Belk. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1995. / Includes bibliographical references (leaves 105-107). / by Jason L. Puchalla. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2009. / Includes bibliographical references (leaf 49). / In this dissertation, I describe the design and construction of a system which can transfer electric power wirelessly. This is accomplished using inductive, near-field, non-radiative coupling between self-resonant copper helices. In our first experiment, we transfered 60W of power over a distance of 2m with 45% efficiency. In our second experiment, we designed a system which can transfer power from a single source to two devices, each 2m away, with 60% total efficiency. We also developed a quantitative model of our helical resonators which predicted the resonant frequency with an accuracy of 5%. / by Robert Alexander Moffatt. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 101-104). / Hadronic jets feature in many final states of interest in modern collider experiments. They form a significant Standard Model background for many proposed new physics processes and also probe QCD interactions at several different scales. At high energies incoming protons produce beam jets. Correctly accounting for the beam and central jets is critical to precise understanding of hadronic final states at the Large Hadron Collider. We study jet cross sections as a function of the shape of both beam and central jets. This work focuses on measuring jet mass but our methods can be applied to other jet shape variables as well. Measuring jet mass introduces additional scales to the collision process and these scales produce large logarithms that need to be resummed. Factorizing the cross section into hard, jet, beam, and soft functions enables such resummation. We begin by studying jet production at e + e- collisions in order to focus on the effects of jet algorithms. These results can be carried over to the more complicated case of hadron collisions. We use the Sterman-Weinberg algorithm as a specific example and derive an expression for the quark jet function. Turning to hadron colliders, we show how the N-jettiness event shape divides phase space into N +2 regions, each containing one central or beam jet. Thus, N-jettiness works as a jet algorithm. Using a geometric measure gives central jets with circular boundaries. We then give a factorization theorem for the cross section fully differential in the mass of each jet, and compute the corresponding soft function at next-to-leading order (NLO). We use a method of hemisphere decomposition, which can also be applied to calculate N-jet soft functions defined with other jet algorithms. Our calculation of the N-jettiness soft function provides the final missing ingredient to extend NLO cross sections to resunmmed predictions at next-to-next-to-leading logarithmic order. We study the production of an exclusive jet together with a Standard Model Higgs boson. Based on theoretical reasons and agreement between our calculation and data from the ATLAS collaboration, we argue that our results for the jet mass spectrum are a good approximation also for inclusive jet production and other hard processes. / by Teppo T. Jouttenus. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 189-206). / Magnetic reconnection is a rapid rearrangement of magnetic line topology in a plasma that can allow magnetic energy to heat, drive macroscopic flows, or accelerate particles in space and laboratory plasmas. Though reconnection affects global plasma dynamics, it depends intimately on small-scale electron physics. In weakly-collisional plasmas, electron pressure anisotropy resulting from the electric and magnetic trapping of electrons strongly affects the structure surrounding the electron diffusion region and the electron current layer. Previous fluid models and simulations fail to account for this anisotropy. In this thesis, new equations of state that accurately describe the electron pressure anisotropy in cases of sufficiently strong guide magnetic field are implemented in fluid simulations and are compared to previous fluid models and kinetic simulations. Elongated current layers in the reconnection region, driven, in part, by this pressure anisotropy, appear as part of a self-regulating mechanism of electron pressure anisotropy. The structure depends on plasma parameters, with low guide fields yielding longer layers. / by Obioma Ogonna Chinyerem Ohia. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 191-198). / The geometry of the kagome lattice leads to exciting novel magnetic behavior in both ferromagnetic and antiferromagnetic systems. The collective spin dynamics were investigated in a variety of magnetic materials featuring spin-1/2 and spin-1 moments on kagome lattices using neutron scattering and thermodynamic probes. Both ferromagnetic and antiferromagnetic systems were studied. Cu(1,3-bdc) is an organometallic material, where the Cu2+ ions form a ferromagnetic S = 1/2. kagomé system. Synthesis techniques were developed to produce -mg-sized deuterated single crystals, and ~2,000 crystals were partially coaligned to create a sample for neutron scattering measurements. Elastic neutron scattering measurements show the existence of long range magnetic ordering below T = 1.77 K. Integrated Bragg peak intensities were analyzed to determine the structure of ordered magnetic moments. Inelastic neutron scattering measurements show the magnon dispersion spectrum, which consists of a flat high energy band and two dispersive, lower energy bands. The application of a magnetic field perpendicular to the kagome plane opens gaps between these three bands and distorts the flatness of the highest energy band. The system was modelled as a nearest-neighbor Heisenberg ferromagnet with Dzyaloshinskii-Moriya(DM) interaction. The model dispersion and scattering structure factor were calculated and fit to the data to precisely determine the strengths of the nearest-neighbor coupling and DM interaction. The observed manon band structure is a bosonic analog to the band structure of the topological insulator systems. Antiferromagnetic kagome systems can exhibit novel magnetic ground states such as quantum spin liquids and spin nematics. Thermodynamic measurements were performed on the antiferromagnetic kagome materials MgxCu₄-x(OH)₆ Cl₂ , featuring S = 1/2 moments. These measurements reveal magnetic ordering at low values of x that is suppressed with increasing x. At x = 0.75, this ordering is not fully suppressed, but susceptibility and specific heat measurements reveal behavior similar to that of the quantum spin liquid candidate herbertsmithite. Thermodynamic and neutron scattering measurements were performed on the kagome lattice material BaNi₃(OH)₂(VO₄)₂, which features S = 1 moments. These measurements reveal competing interactions, which result in a spin glass ordering transition. / by Robin Michael Daub Chisnell. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 111-115). / In this thesis, I present three results on quantum algorithms and their complexity. The first one is a numerical study on the quantum adiabatic algorithm( QAA) . We tested the performance of the QAA on random instances of MAX 2-SAT on 20 qubits and showed 3 strategics that improved QAA's performance, including a counter intuitive strategy of decreasing the overall evolution time. The second result is a security proof for the quantum money by knots proposed by Farhi et. al. We proved that quantum money by knots can not be cloned in a black box way unless graph isomorphism is efficiently solvable by a quantum computer. Lastly we defined a modified quantum query model, which we called bomb query complexity B(J), inspired by the Elitzur-Vaidman bomb-testing problem. We completely characterized bomb query complexity be showing that B(f) = [Theta](Q(f)2 ). This result implies a new method to find upper bounds on quantum query complexity, which we applied on the maximum bipartite matching problem to get an algorithm with O(n1.75) quantum query complexity, improving from the best known trivial O(n2 ) upper bound. / by Han-Hsuan Lin. / Ph. D.