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DisciplineGraduate College (401)

Physics (401)

AuthorsVisscher, Koen (29)Su, Shufang (24)Shupe, Michael (22)Melia, Fulvio (15)Bowen, Theodore (14)Hill, Henry A. (14)Mazumdar, Sumit (14)Mazumdar, Sumitendra (14)Manne, Srinivas (13)Stafford, Charles (13)View MoreTypestext (401)Dissertation-Reproduction (electronic) (284)Electronic Dissertation (117)
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Numerical solutions of lattice quantum fields with a hierarchy of Schroedinger-like equations.

Ludwig, Mark Allen. (The University of Arizona., 1990)

Systems of quantized fields can be described by an infinite hierarchy of coupled equations. Such a hierarchy is derived from first principles for a simple interacting field theory to illustrate this type of a representation. The perturbation series for the S matrix is derived from the hierarchy equations in order to show its equivalence to the usual expansion in Feynman amplitudes. An inquiry is then conducted to determine whether this type of representation is useful for solving problems. Truncations of the hierarchy which predict simple bound states are examined in the weak coupling limit, and equations describing a hydrogen-like atom are obtained. Next, the numerical approximation of a truncated hierarchy is studied, and a scattering/particle creation process is modeled in one dimension with a resulting accuracy of 1 to 2 percent. Finally, the mathematical questions of convergence which arise in connection with quantized fields are discussed within the context of the hierarchy equations.

Applications of Effective Field Theories for Precision Calculations at e⁺e⁻ Colliders

Fickinger, Michael (The University of Arizona., 2012)

Effective field theories can be used to describe measurements at e⁺e⁻ colliders over a wide kinematic range while allowing reliable error predictions and systematic extensions. We show this in two physical situations. First, we give a factorization formula for the e⁺e⁻ thrust distribution dσ/dτ with thrust T and τ = 1 − T based on soft collinear effective theory. The result is applicable for all τ, i.e. in the peak, tail, and far-tail regions. We present a global analysis of all available thrust distribution data measured at center-of-mass energies Q = 35 to 207 GeV in the tail region, where a two parameter fit to the strong coupling constant α(s)(m(Z)) and the leading power correction parameter Ω₁ suffices. We find α(s)(m(Z)) = 0.1135 ± (0.0002)expt ± (0.0005)hadr ± (0.0009)pert, with x²/dof = 0.91, where the displayed 1-sigma errors are the total experimental error, the hadronization uncertainty, and the perturbative theory uncertainty, respectively. In addition, we consider cumulants of the thrust distribution using predictions of the full spectrum for thrust. From a global fit to the first thrust moment we extract α(s)(m(Z)) and Ω₁. We obtain α(s)(m(Z)) = 0.1140 ± (0.0004)exp ± (0.0013)hadr ± (0.0007)pert which is compatible with the value from our tail region fit. The n-th thrust cumulants for n ≥ 2 are completely insensitive to Ω₁, and therefore a good instrument for extracting information on higher order power corrections, Ω'(n)/Qⁿ, from moment data. We find (˜Ω₂)^1/2 = 0.74 ± (0.11)exp ± (0.09)pert GeV. Second, we study the differential cross section dσ/dx of e⁺e⁻-collisions producing a heavy hadron with energy fraction x of the beam energy in the center-of-mass frame. Using a sequence of effective field theories we give a definition of the heavy quark fragmentation function in the endpoint region x → 1. From the perspective of our effective field theory approach we revisit the heavy quark fragmentation function away from the endpoint and outline how to develop a description of the heavy quark fragmentation function valid for all x. Our analysis is focused on Z-boson decays producing one B-meson. Finally, we will give a short outlook of how we want to apply our approach to determine the leading nonperturbative power corrections of the b-quark fragmentation function from LEP experiments.

Characterization of the one-dimensional fractal structures by correlations, cumulants and moments as applied to high-energy hadronic rapidity correlations.

Hakioglu, Tugrul T. (The University of Arizona., 1991)

In this dissertation we investigate the question that high energy irregular rapidity events can be generated by finite samples of one dimensional fractal structures. The idea is basically to generate a rapidity histogram by transforming a one-dimensional map of which the histogram is known and simple a one-dimensional map with the desired histogram. Then studying the system in different dynamical regimes we analyse the properties of factorial moments, cumulants and multifractal properties. It is useful to have such models in the sense that one then has a direct ability to check some of the quantitative features that can be distinguished from each other because they refer to different dynamical regimes (i.e. intermittency and chaos). In studying such models we analyse the qualitative and quantitative features of the question of hadronic intermittency in comparison with the same features in those models both theoretically and experimentally. We finally made an analogy with the field theory formalism of hadron production and Quantum Optics in which the question of regularity vs. irregularity has been asked much earlier.

Thermalization theory in heavy ion collisions by nonequilibrium statistical mechanics.

Abu-Samreh, Mohammad Mahmud. (The University of Arizona., 1991)

This dissertation presents a semiclassical microscopic approach based on the Uehling-Uhlenbeck equation for studying the equilibration processes due to nucleon-nucleon collisions during the collision of two heavy ions in the low and intermediate energy domain (5-100 MeV/nucleon). The state formed in the early stages of a heavy-ion collision can be characterized by a highly excited non-equilibrium system of nucleons. Equilibration processes then take place resulting in a system for which a temperature can be defined at least locally. The single-nucleon distribution function for the nucleons during the early stage of the ion-ion collision is represented in momentum-space either by two Fermi-spheres separated by the relative momentum of the impacting ions or by a deformed Fermi-sphere. The equilibration (thermalization) of this initial distribution in momentum-space is studied by calculating the collision term as a function of time. The relaxation-times are investigated through a microscopic model that incorporates the UU collision term with the relaxation-time approximation. Relaxation-times for the equilibration are obtained as a function of density and temperature. The temperature dependence is strong at low temperatures and this is a consequence of the Fermi statistics. The mode dependence of the relaxation-times is also calculated by expanding the angular dependence of the distribution in spherical harmonics. The RTA is also tested against thermalization of the Fermi-sphere systems and is found to be reasonable. Transport coefficients for viscosity, thermal conductivity and diffusion are also calculated as well as their temperature and density dependencies. Their relation to relaxation-times are derived. The mean free path of nucleons in hot nuclear matter is also studied in the same frame of work. The numerical calculations of the collision term are an important part of this investigation. They involve five-dimensional integrations carried out using Gaussian and Simpson's numerical methods.

THE ROLE OF POLYCYCLIC AROMATIC HYDROCARBONS IN THE STUDY OF FULLERENE FORMATION

Zumwalt, Michael Crane (The University of Arizona., 1995)

Two approaches intended to elucidate the fullerene-formation mechanism are presented. The first of these involves pyrolytic synthesis of fullerenes from hydrocarbon ring structures known as polycyclic aromatic hydrocarbons (PAH's). Following work by Taylor et al. (Nature 366, 728, 1993), C60 is be made by heating a naphthalene vapor/argon mixture to approximately 1000°C. The use of several precursor P AH' s, including naphthalene, is examined in this work. The second approach involves the intentional poisoning of carbon-arc fullerene production by the addition of hydrogen (H₂) to the quenching atmosphere. By adding hydrogen in varying amounts one produces both PAH's and chain molecules, possibly representing interrupted steps of the pathway leading to fullerenes. Various analytical techniques are employed to examine both approaches. It is shown by mass spectrometry' that pyrolytic synthesis is not indicative of the fullerene-formation mechanism of the carbon-arc technique pioneered by Krlitschmer et al. (Nature 347, 354, 1990). In addition to mass spectrometry, Fourier-transform infrared and ultra-violet/visible absorption spectroscopy, high-performance Iiquidchromatography, and Raman-scattering spectroscopy are brought to bear in the analysis of the hydrogen-poisoning approach. From the analysis the PAH molecules formed in the hydrogen poisoning of the carbon-arc do not appear to comprise a pathway to fullerene formation. However, there is evidence indicating that chains, produced as a result of hydrogen contamination of the carbon-arc technique, are related to the formation of fullerene molecules.

Testing General Relativity in the Strong-Field Regime with Observations of Black Holes in the Electromagnetic Spectrum

Johannsen, Tim (The University of Arizona., 2012)

General relativity has been tested by many experiments, which, however, almost exclusively probe weak spacetime curvatures. In this thesis, I create two frameworks for testing general relativity in the strong-field regime with observations of black holes in the electromagnetic spectrum using current or near-future instruments. In the first part, I design tests of the no-hair theorem, which uniquely characterizes the nature of black holes in terms of their masses and spins in general relativity and which states that these compact objects are described by the Kerr metric. I investigate a quasi-Kerr metric and construct a Kerr-like spacetime, both of which contain an independent parameter in addition to mass and spin. If the no-hair theorem is correct, then any deviation from the Kerr metric has to be zero. I show that already moderate changes of the deviation parameters in either metric lead to significant modifications of the observed signals. First, I apply this framework to the imaging of supermassive black holes using very-long baseline interferometry. I show that the shadow of a black hole as well as the shape of a bright and narrow ring surrounding the shadow depend uniquely on its mass, spin, inclination, and the deviation parameter. I argue that the no-hair theorem can be tested with observations of the supermassive black hole Sgr A*. Second, I investigate the potential of quasi-periodic variability observed in both galactic black holes and active galactic nuclei to test the no-hair theorem in two different scenarios. Third, I show that the profiles of relativistically broadened iron lines emitted from the accretion disks of black holes imprint the signatures of deviations from the Kerr metric. In the second part, I devise a method to test the predicted evaporation of black holes in the Randall-Sundrum model of string theory-inspired braneworld gravity through the orbital evolution of black-hole X-ray binaries and obtain constraints on the size of the extra dimension from A0620-00 and XTE J1118+480. I predict the first detection of orbital evolution in a black-hole binary.

Nuclear and molecular processes in muon-catalyzed fusion.

Harley, David. (The University of Arizona., 1991)

The dt-αn continuum in the presence of the muon is studied in detail, and it is shown that the existence of extended continuum states just beneath the d+(tμ)₁(s) threshold can lead to a variety of 'pseudoresonant' fusion processes with a temperature and density dependence distinct from those leading to molecular formation. Various in-flight and pseudoresonant fusion reaction cross sections involving the excitation of electromolecular states and two or three scattering bodies are computed. Fusion processes in very dense plasmas of ∼10³ liquid hydrogen density are studied, and it is shown that in this environment both sticking and muon transfer problems are eliminated, and that pseudoresonant fusion processes should dominate. In this context, the use of negatively charged hadrons as potential catalytic particles is also considered.

Intermittency, moments and correlations in distributions of particles created in high-energy collisions.

Eggers, Hans Christoph. (The University of Arizona., 1991)

Intermittency, as introduced into multiparticle production by Bialas and Peschanski, has become a fruitful and rapidly growing industry. The original concept of intermittency in the form of the Alpha model is discussed in detail and suggestions for extensions are made. We analyze the factorial moments measured by different experimental collaborations in terms of their nontrivial many-particle correlations, the cumulants. A large fraction of measured moments is shown to originate in two-particle correlations. The validity of the Linked Pair ansatz is tested and found to be acceptable to fourth order for hadronic collisions but uncertain for nuclear collisions. A cumulant decomposition for bin-bin correlations is derived, and a general formalism is developed for treating correlations of particle distributions consisting of several distinct populations, such as particles of different charge.

Diffusion in the Io plasma torus and its relation to the torus spatial structure.

Davis, Eric Wesley. (The University of Arizona., 1991)

This is a study of the plasma diffusion processes relevant to the physical nature of the Io plasma torus at Jupiter. A knowledge of the diffusion processes involved in the Io plasma torus is essential to an understanding of the spatial structure and energetics of the torus. The only published theory of Io torus plasma diffusion, centrifugally driven flux tube interchange instability, is based on turbulent plasma interchange instability. We have examined physical properties that lead us to conclude that flux tube interchange diffusion is not a valid mechanism in the plasma torus. The collisional nature of the hot torus plasma is seen through its observed EUV emissions which dominate the energy loss from the system. Further, the torus plasma parameters fall in the range of values satisfying the criteria for the use of collisional transport theory to derive a collisional diffusion coefficient. The collisional nature of the torus plasma is characterized in the long mean free path regime where classical transport theory breaks down. We study the Chapman-Enskog method of calculating the plasma diffusion coefficient from a solution of the Boltzmann equation. Simplifying approximations of a fully ionized plasma dominated by Coulomb elastic charged particle collisions are made to derive an ad hoc non-classical diffusion coefficient which results in slow differential diffusion rates for the various sulfur and oxygen ions in the plasma torus. The radial spatial structure and energetics of the plasma torus is modeled by employing the collisional diffusion coefficient in a computer model calculation of collisional ionization-diffusive equilibrium and energy branching. The computer model employs the known significant plasma reactions involving the torus sulfur and oxygen species, utilizing the most recently available atomic parameters. In view of the failure of Neutral Cloud Theory to adequately power the copious amounts of UV radiation emitted by the Io plasma torus, we employed the radial plasma model to investigate this "energy crisis." Toward this end, we investigate the application to our plasma model of a proposed heterogeneous source of energetic electrons and a proposal of inward diffusing energetic outer-magnetospheric OII and SII ions as ad hoc heat inputs to the plasma torus electrons, in order to maintain a steady state energy balance.

Atmospheres of comets: Gas dynamic models and inference of kinematic parameters

Hu, Hongyao. (The University of Arizona., 1991)

Cometary nuclei may be our best available probes of the physical and chemical nature of the presolar nebula. However, in situ sampling of cometary nuclei to determine their composition is generally not feasible. Instead, remote spectroscopic observations of cometary comae are used to infer cometary composition. This approach relies on one's ability to model accurately the density distributions of gas and dust in the comae and a complex network of photochemical and molecular processes. Previously, a variety of theoretical models had been developed and, unfortunately, they are applicable only to a portion of the coma or to specific problems. In the first part of this thesis we introduce a preliminary version of a gas model built upon the concepts of dilute gas theory. This model is valid over the whole coma and it incorporates all previous models as its special cases, thus providing a new theoretical foundation for future cometary studies. In the second part of the thesis we discuss a spectral outflow model. This model is a special case of the dilute gas model and is tailored specifically to retrieve kinematic properties of cometary comae from velocity-resolved spectral line profiles. We review the formation of cometary spectral line profiles and we develop an analytic expression that maps three dimensional number density distributions into synthetic spectral line profiles. After discussing simplifications and Monte Carlo computational procedures, we apply the spectral outflow model to interpret infrared observations of H₂O in comets Halley and Wilson.

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