Thesis (M.S.) Massachusetts Institute of Technology. Dept. of Physics, 1951. / Bibliography: leaf 27. / by William Hargrove Lewis. / M.S.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 142-153). / This thesis reports on progress in understanding the set of 6D F-theory vacua. F-theory provides a strikingly clean correspondence between physics and physical quantities and mathematics and geometrical quantities, which allows us to make precise mathematical statements using well defined and understood methods. We present two related results that both serve the following principal goal: to understand the set of 6D F-theory vacua using geometrical methods, and then to compare these to low-energy supergravities. In doing so, we find a near-perfect correspondence between low-energy supergravities that can be obtained from F-theory and field theories that satisfy known low-energy consistency conditions, e.g. anomaly cancellation. However, we will also isolate several cases that we prove can never arise in F-theory yet have no visible lowenergy inconsistencies. The results are presented in two chapters. First, we describe a complete, systematic enumeration of all elliptically fibered Calabi-Yau threefolds (EF CY3s) with Hodge number h²,¹ >/= 350; physically, this classifies all F-theory models that lead to low-energy supergravities with >/= 351 neutral hypermultiplets. This result is obtained using global geometric calculations in finitely many, specific geometries. Second, we classify which local geometrical structures, corresponding to combinations of gauge algebras and (potentially shared) matter, can arise in F-theory. This classification is performed using local geometric calculations. This investigation reveals an exceedingly tight correspondence between F-theory models and consistent low-energy supergravities. Indeed, this near-perfect agreement provides a backdrop against which discrepancies between F-theory and low-energy supergravities stand out in sharp contrast. We describe in detail these discrepancies, in which seemingly consistent field theories cannot be described in F-theory. This work has several implications. First, it further refines the understanding of 6D supergravity models in F-theory, which has implications for string universality in 6D. It adds a level of mathematical precision to the study of 6D superconformal field theories (SCFTs) begun in [4, 3], which is a conjecturally complete classification of all 6D SCFTs. Our analysis confirms many of their results, but also explicitly shows that some of their proposed models cannot in fact be realized through their construction. Since our results can be phrased in terms of geometry, they also have implications for the study of EF CY3s. Finally, we discuss the subset of our results that hold in 4D F-theory as well, where they provide additional structure in a still difficult-to-constrain landscape. / by Samuel Buck Johnson. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Includes bibliographical references (245-255). / by Theodore W. Sung. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 167-176). / Quantum mechanics has led not only to new physical theories, but also a new understanding of information and computation. Quantum information not only yields new methods for achieving classical tasks such as factoring and key distribution but also suggests a completely new set of quantum problems, such as sending quantum information over quantum channels or efficiently performing particular basis changes on a quantum computer. This thesis contributes two new, purely quantum, tools to quantum information theory-coherent classical communication in the first half and an efficient quantum circuit for the Schur transform in the second half. The first part of this thesis (Chapters 1-4) is in fact built around two loosely overlapping themes. One is quantum Shannon theory, a broad class of coding theorems that includes Shannon and Schumacher data compression, channel coding, entanglement distillation and many others. The second, more specic, theme is the concept of using unitary quantum interactions to communicate between two parties. We begin by presenting new formalism: a general framework for Shannon theory that describes communication tasks in terms of fundamental information processing resources, such as entanglement and classical communication. Then we discuss communication with unitary gates and introduce the concept of coherent classical communication, in which classical messages are sent via some nearly unitary process. We find that coherent classical communication can be used to derive several new quantum protocols and unify them both conceptually and operationally with old ones. / (cont.) Finally, we use these new protocols to prove optimal trade-o curves for a wide variety of coding problems in which a noisy channel or state is consumed and two noiseless resources are either consumed or generated at some rate. The second half of the thesis (Chapters 5-8) is based on the Schur transform, which maps between the computational basis of (Cd)n and a basis (known as the Schur basis) which simultaneously diagonalizes the commuting actions of the symmetric group Sn and the unitary group Ud. The Schur transform is used as a subroutine in many quantum communication protocols (which we review and further develop), but previously no polynomial-time quantum circuit for the Schur transform was known. We give such a polynomial-time quantum circuit based on the Clebsch-Gordan transform and then give algorithmic connections between the Schur transform and the quantum Fourier transform on Sn. / by Aram Wettroth Harrow. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2014. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 75-78). / New images from the Hubble Space Telescope of the FRII radio galaxy Pictor A reveal a number of jet knot candidates which coincide with previously detected radio and x-ray knots. Previous observations in x-ray and radio bands show the entire jet to be 1.90 long, with interesting variability, but an optical component was previously unknown. The discovered optical component is faint, and knot candidates must be teased out from a bright host galaxy. Using three broadband lters, we extract knot fluxes and upper-bounds on the ux for multiple knot candidates at wavelengths of 1600nm, 814nm and 475nm. We nd that the data suggest that localized particle re-accleration events followed by synchrotron emission could explain the observed knot candidates, but those electrons could not supply enough x-ray ux to match prior observations. Our data provide key evidence suggesting a second, higher energy electron population which was previously hypothesized, but could not be confirmed. / by Eric S. Gentry. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005. / "June 2005." / Includes bibliographical references (p. 181-184). / In this thesis I present the design and experimental demonstration of the first photonic band gap (PBG) accelerator at 17.140 GHz. A photonic band gap structure is a one-, two- or three-dimensional periodic metallic and/or dielectric system (for example, of rods), which acts like a filter, reflecting rf fields in some frequency range and allowing rf fields at other frequencies to transmit through. Metal PBG structures are attractive for the Ku-band accelerators, because they can be employed to suppress wakefields. Wakefields are unwanted modes affecting the beam propagation or even destroying the beam. Suppression of wakefields is important. In this thesis, the theory of metallic PBG structures is explained and the Photonic Band Gap Structure Simulator (PBGSS) code is presented. PBGSS code was well benchmarked and the ways to'benchmark the code are described. Next, the concept of a PBG resonator is introduced. PBG resonators were modelled with Ansoft HFSS code, and a single-mode PBG resonator was designed. The HFSS design of a travelling-wave multi- cell PBG structure was performed. The multicell structure was built, cold-tested and tuned. Finally, the hot-test PBG accelerator demonstration was performed at the accelerator laboratory. The PBG accelerating structure was installed inside a vacuum chamber on the Haimson Research Corporation (HRC) accelerator beam line and powered with 2 MW from the HRC klystron. The electron bunches were produced by the HRC accelerator. The electron beam was accelerated by 1.4 MeV inside the PBG structure. / by Evgenya I. Smirnova. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2004. / Includes bibliographical references (leaves 71-73). / We describe the attenuation of the second vowel formant peak near the second resonance of the subglottal system, and test whether it is a quantal acoustic-articulatory relation (Stevens 1972, 1989) dividing front and back vowels. We find strong evidence for this hypothesis within English and cross-linguistically, and illustrate one way to test proposed quantal relations. / by Morgan A. Sonderegger. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 39-40). / Dirac particles can exhibit Hall-like transport induced by Berry's gauge field in the absence of magnetic field. We develop a detailed picture of this unusual effect for charge carriers in graphene nanostructures. The Hall effect is nonzero in each valley but is of opposite signs in different valleys, giving rise to charge-neutral valley currents. Our analysis reveals that p-n junctions in graphene support persistent valley currents that remain nonzero in the system ground state (in thermodynamic equilibrium). The valley currents can be controlled via the bias and gate voltages, enabling a variety of potentially useful valley transport phenomena. / by Polnop Samutpraphoot. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2015. / In title on title-page, " [beta][beta][tau][tau]" appear as the lower-case Greek letters. Cataloged from PDF version of thesis. / Includes bibliographical references (pages 63-66). / A measurement of standard model Higgs pair production in [beta][beta][tau][tau] final states at the High Luminosity LHC is investigated. Higgs pair production can be used to measure the Higgs trilinear coupling constant, which uniquely determines the shape of the Higgs potential. The doubly hadronic, hadron-muon, and hadron-electron di-[tau] final states are considered, with a shape analysis on either the stransverse mass (doubly hadronic) or a BDT discriminant (hadron-muon, hadron-electron) distribution performed to extract expected significances. The expected 95% CL upper limit on the cross section times branching ratio from a combination of all three channels is 2.2 times the SM value, with an expected +1[sigma] uncertainty on the measured cross section of 67%, indicating this measurement is feasible. / by Jay Mathew Lawhorn. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006. / Includes bibliographical references (p. 77-81). / In this thesis we present some works done during my doctoral studies. These results focus on two directions. The first one is motivated by tachyon dynamics in open string theory. We calculate the stress tensors for the p-adic string model and for the pure tachyonic sector of open string field theory (OSFT). We give the energy density of lump solutions and attempt to evaluate the evolution of the pressure in rolling tachyon solutions. We discuss the relevance of the pressure calculation for the identification of the large time solution with a gas of closed strings. In the second direction, we give some results in closed string field theory (CSFT). We considered marginal deformations in CSFT. The marginal parameter, called a, is that associated with the dimension-zero primary operator cWcX&X. We use this marginal operator to test the quartic structure of CSFT and the feasibility of level expansion. We check the vanishing of the effective potential for a. In the level expansion the quartic terms generated by the cubic interactions must be canceled by the elementary quartic interaction of four marginal operators. We confirm this prediction, thus giving evidence that the sign, normalization, and region of integration Vo,4 for the quartic vertex are all correct. / (cont.) This is the first calculation of an elementary quartic amplitude for which there is an expectation that can be checked. We also extend the calculation to the case of the four marginal operators associated with two space coordinates. We then try to search a critical point of the tachyon potential in CSFT. We include the tachyon, the dilaton, and massive fields in the computation. Some evidence is found for the existence of a closed string tachyon vacuum. It seems that this critical point becomes more shallow when higher level contributions are considered. We also relate fields in the sigma model and those in CSFT. Moreover, large dilaton deformations are studied numerically. Finally, we use the low-energy effective field equations that couple gravity, the dilaton, and the bulk closed string tachyon to study the end result of the physical decay process associated with the instability of closed string tachyon. We establish that whenever the tachyon induces the rolling process, the Einstein metric undergoes collapse while the dilaton rolls to strong coupling. Some more general potentials and the possible cosmological application are discussed. / by Haitang Yang. / Ph.D.