In this thesis, I investigate in detail two basic problems in nonequilibrium statistical mechanics. First, if a spin system such as a kinetic Ising model or a kinetic Potts model is quenched from supercritical temperature to subcritical temperature, how does the system coarsen, and what complexities arise as the system descends in energy toward one of its equilibrium states? Second, if a kinetic Ising model is evolved from a deterministic initial condition at zero temperature, how do the domain interfaces evolve in time? I first study the nonconserved coarsening of the kinetic spin systems mentioned above. The coarsening of a 2d ferromagnet can be described exactly by an intriguing connection with continuum critical percolation. Furthermore, careful simulations of phase ordering in the 3d Ising model at zero temperature reveal strange nonstatic final states and anomalously slow relaxation modes, which we explain in detail. I find similarly rich phenomena in the zero-temperature evolution of a kinetic Potts model in 2d, where glassy behavior is again manifest. We also find large-scale avalanches in which clusters merge and dramatically expand beyond their original convex hulls at late times in the dynamics. Next, I study the geometrically simpler problem of the evolution of a single corner interface in the Ising model. We extend prior work by investigating the Ising Hamiltonian with longer interaction range. We solve exactly the limiting shapes of the corner interface in 2d for several interaction ranges. In 3d, where analytical treatments are notoriously difficult, we develop novel methods for studying corner interface growth. I conjecture a growth equation for the interface that agrees quite well with simulation data, and I discuss the interface's surprising geometrical features. In the summary, I discuss the broader implications of our findings and offer some thoughts on possible directions for future work.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 181-184). / Inclusive electron scattering experiments using fixed targets are an important tool for studying the structure of the nucleons. The electromagnetic structure of the proton, as encapsulated by its elastic form factors, can be extracted through measurements of the elastic electron-proton scattering cross-section. The GMp experiment in Hall A at the Thomas Jefferson National Accelerator Facility (JLab) seeks to measure this cross-section with high precision up to large momentum transfers. In addition, it is known that the inelastic structure of the nucleon is modified inside the nucleus. This modification, known as the EMC effect, can be studied using inclusive electron Deep Inelastic Scattering (DIS) on a nuclear target. Evidence suggests that the EMC effect may arise due to nucleon Short Range Correlations (SRC). This thesis describes studies of the elastic proton form factor measured in the GMp experiment at Hall A of JLab and studies of the EMC effect in nuclei relative to deuterium using data collected at the CLAS detector in Hall B at JLab. Furthermore, this works presents new measurements of SRC pair abundances in nuclei and develops a data-driven SRCbased phenomenological model of the EMC effect, which can correctly describe the effect across nuclei. / by Barak Schmookler. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 165-173). / Charged-hadron pseudorapidity densities and multiplicity distributions in protonproton collisions at [the square root of sigma] = 0.9, 2.36, 7.0 TeV were measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield was obtained by counting the number of hit-pairs (tracklets). The charged-particle multiplicity per unit of pseudorapidity dNch/d[eta] [eta]<0.5 at [the square root of sigma] = 7.0 TeV is 5.78 i 0.01(stat.) i 0.23(syst.) for nonsingle- diffractive events, higher than predicted by commonly used models. The relative increase in charged-particle multiplicity from [the square root of sigma] = 0.9 to 7 TeV is 66.1% ± 1.0%(stat.) ± 4.2%(syst.) and strong KNO violation is observed in the multiplicity distributions. Results are compared with low energy measurements. / by Yen-Jie Lee. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1997. / Includes bibliographical references. / by Marc-Oliver Mewes. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2006. / Includes bibliographical references (leaf 25). / One of the largest problems in scanning tunneling microscopy design is noise control. It is the burden of the designer to determine if money should be used to build a floating room for vibration isolation or for top-of-the-line preamplifiers that can be placed at low temperatures. This thesis presents a simulation of the STM measurement chain, from tunneling tip to computer control. The goal is to see how noise at different stages of the measurement chain affect the output of spectroscopy (density of states) measurements. Specifically, we look at how spectroscopy measurements depend on the temperature of the sample, the density of states in the sample and tip, the shakiness of the tip, the noise present in the current preamplifier, and several other settings. Chapter 1 describes STM spectroscopy measurement, Chapter 2 explains how it is simulated, and Chapter 3 finally looks at the results of various simulations. / by Vivek Venkatachalam. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006. / Includes bibliographical references (p. 171-184). / This thesis presents three studies of warm (photoionized) absorber variability in Active Galactic Nuclei (AGN) using high-resolution X-ray spectra provided by the Chandra High Energy Transmission Grating (HETG). The first study is a single observation of the AGN MR 2251-178, which is known to have a highly variable warm absorber (WA). We find an unusually thin effective hydrogen column density along the line of sight compared to previous observations. Strong line emission without corresponding absorption indicates significant WA geometric structure. Strong absorption features in the spectrum are evidence of a highly-ionized, high-velocity outflow, which could be carrying a large amount of mass and energy out of the AGN. In the second study, we search for absorption lines variability in the well-studied WA of MCG -6-30-15. We find a significant anti-correlation over time between at least two ions, with suggestions of additional time variation in other ions. At least one line, the is - 2p resonance line of Mg XII, varies as a function of 2-10 keV continuum luminosity. Luminosity-driven ionization changes alone are insufficient to explain the observed variation. / (cont.) Either multiple factors influence line strength on observable time scales, or the line of sight to the central source varies over time through a structured absorber. In the third study, we survey spectra from the HETG data archive. We model the normalized excess variance (NEV) spectrum of a varying WA and find that it does not explain high-energy (> 2 keV) spectral variation, nor does it generally fit NEV spectra at lower energies (< 2 keV). We also search through each spectrum at high resolution (AA = 0.01 A) for bins which vary more than expected due to normal Poissonian fluctuations. We find some evidence for such variation in the aggregate sample, though not in AGN individually. Our results show that WA structure is more complicated than pictured in contemporary models. Future high-resolution spectroscopic variability studies are certainly warranted. AGN models should eventually consider the effects of WA structure and the influence of continuum variation on the WA. / by Robert R. Gibson. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2007. / Includes bibliographical references (p. 93-95). / Understanding the states in the vicinity of the Mott insulator is crucial to understanding both the physics of the transition between a Mott insulating phase and a metallic phase and the physics of the cuprate high-temperature superconductors. In this thesis, we start from the standard Mott insulating regime of the two dimensional Hubbard model. We then study the physics of nearby states where transport has been restored. First we consider doping of the Hubbard model in the strong coupling limit, i.e. the t-J model. Using the variational Monte Carlo technique, we study Gutzwiller projected states. In particular, studying the projected BCS quasiparticles, we calculate the renormalization of the quasipaticle current and the spectral weight. Both are investigated as a function of momentum and doping. Finally, we discuss the relation between this model and the cuprate superconductors. In the second half of this thesis, we return to the half-filled Hubbard model but now at intermediate values of U/t. In this regime, we study the spin liquid phase, a state that possibly lives between the Mott insulator and the normal metal. Motivated by the recently created organic compound r-(BEDT-TTF)2- Cu2(CN)3, we study a particular spin liquid where there is a spinon Fermi surface coupled to a U(1) gauge field. While still a charge insulator, this model has many metallic-like properties. We first develop a quantum Boltzmann equation for this model from which we calculate the spin resistivity and the more experimentally accessible thermal conductivity. We then proceed to consider spinon pairing and calculate the gauge field contribution to the spin susceptibility. We find that the theoretical result is consistent with experiments giving further evidence that at low temperatures this compound is described by this particular U(1) spin liquid. / by Cody Patrick Nave. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005. / Includes bibliographical references (leaf 18). / Introduction: In this paper, I will be assessing the capabilities of the Neutral Meson Spectrometer (NMS) detector in a planned experiment at the High Intensity Gamma Source at Duke University. I will review the relevant theory and set out the importance of this experiment. I will describe the proposed apparatus and how I have modeled it in my simulation. I will explain the data we wish to draw from the experiment and present results as to how well I believe this setup will perform. / by Ethan Howe. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2006. / Includes bibliographical references (p. 81-86). / For many years, it was thought that Landau's theory of symmetry breaking could describe essentially all phases and phase transitions. However, in the last twenty years, it has become clear that at zero temperature, quantum mechanics allows for the possibility of new phases of matter beyond the Landau paradigm. In this thesis, we develop a general theoretical framework for these "exotic phases" analogous to Landau's framework for symmetry breaking phases. We focus on a particular type of exotic phase, known as "topological phases", and a particular physical realization of topological phases - namely frustrated quantum magnets. Our approach is based on a new physical picture for topological phases. We argue that, just as symmetry breaking phases originate from the condensation of particles, topological phases originate from the condensation of extended objects called "string-nets." Using this picture we show that, just as symmetry breaking phases can be classified using symmetry groups, topological phases can be classified using objects known as "tensor categories." / (cont.) In addition, just as symmetry breaking order manifests itself in local correlations in a ground state wave function, topological order manifests itself in nonlocal correlations or quantum entanglement. We introduce a new quantity - called "topological entropy" - which measures precisely this nonlocal entanglement. Many of our results are applicable to other (non-topological) exotic phases. / by Michael Aaron Levin. / Ph.D.

This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2007. / Includes bibliographical references (p. 153-167). / (cont.) These findings impose a serious problem on particle heating and acceleration within ICMEs. Both case studies and superposed epoch analysis demonstrate that plasma depletion layers (PDLs) and mirror-mode waves occur in the sheath regions of ICMEs with preceding shocks. A theoretical analysis shows that shock-induced temperature anisotropies can account for many observations made in interplanetary shocks, planetary bow shocks and the termination shock in the heliosphere. A comparative study of these shocks and corresponding sheaths reveals some universal processes, such as temperature anisotropy instabilities, magnetic field draping and plasma depletion. These results underscore important physical processes which alter the ICME environment. / This thesis studies the evolution of coronal mass ejections (CMEs) in the solar wind. We develop a new method to determine the magnetic field orientation of CMEs using Faraday rotation. A radio source occulted by a moving magnetic flux rope gives two basic Faraday rotation curves, consistent with Helios observations. The axial component of the magnetic field produces a gradient in the Faraday rotation pattern obtained from multiple radio sources along the flux rope, which allows us to determine the CME field orientation and helicity 2 - 3 days before CMEs reach the Earth. We discuss implementation of the method by the Mileura Widefield Array. We present the first direct evidence that magnetic clouds (MCs) are highly flattened and curved due to their interaction with the ambient solar wind. The cross- sectional aspect ratio of MCs is estimated to be no smaller than 6 : 1. We offer a simple model to extract the radius of curvature of the cross section. Application of the model to observations shows that the cross section tends to be concave-outward at solar minimum while convex-outward near solar maximum. CMEs expand in the solar wind, but their temperature decreases more slowly with distance than an adiabatic profile. The turbulence dissipation rate, deduced from magnetic fluctuations within interplanetary CMEs (ICMEs), seems sufficient to produce the temperature profile. We find that the ICME plasma is collision dominated and the alpha-proton differential speed is quickly reduced. However, the alpha particles are preferentially heated with a temperature ratio Ta/Tp = 4 - 6. / by Ying Liu. / Ph.D.