 Physics
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Senior Projects |
| Physics Courses Faculty Research Events | 2000 |
Senior Projects - Class of 2000
The nature of dark matter is currently one of the most important puzzles of Astrophysics. Big bang nucleosynthesis suggests that WB = 0 05 + 0 005, whereas WM is measured to be 0.35 + 0.1, where Wx is defined as the density of x divided by the critical mass density of the universe. Non-baryonic matter must make up the difference. Particle physics theories provide a couple of possible candidates, in the form of relic elementary particles left over from the big bang. One such candidate is a Weakly Interacting Massive Particle (WIMP) of mass between 50 and 500 GeV. The Cryogenic Dark Matter Search (CDMS) collaboration, which includes Prof Akerib's group here at CWRU, has developed a novel technique for Earth-based detection of WIMPs from our own galactic halo. By simultaneously measuring the charge liberated and phonon energy deposited in a germanium detector when a particle interacts with the detector, one can distinguish between WIMP events (nuclear recoils) and electromagnetic background events (electron recoils). As the CDMS project shifts from development to fill production and fabrication of detectors, the detectors developed will have to be calibrated and have their performance fully characterized. This thesis will address one of the performance criteria for study, such as the detector response to a specific form of radiation, e.g., from a radioactive source.
Distance measurements to Type Ia supernovae (SNe Ia) suggest that the expansion rate of the universe is increasing with time, contrary to previous beliefs about the evolution of the universe. One mechanism that could account for this acceleration is vacuum energy, also referred to as the cosmological constant, which would exert a large, negative pressure counteracting the deceleration effects of gravity. The uncertainty in the measurements made of supernovae at various redshifts will be examined in order to determine at which redshifts supernovae observations should be made to most efficiently place constraints on the vacuum energy. In addition, we will explore how strategies may vary depending upon how these uncertainties vary as a function of redshift, and also depending on which physical questions one wishes to probe.
David Olson with Glenn Starkman
Recently, there has been much excitement in the cosmology community over the results coming from surveys of Type Ia supernovae. These surveys seem to indicate that the rate of expansion of the universe (as measured by the relationship between the redshifts of the supernovae and their luminosity distances) is accelerating. These observations extend out to a redshift of approximately 1.2. Recently, however, Starkman, Trodden and Vachaspati have shown that in order to conclude that this expansion is a sign that the universe is inflating one must first extend these observations at least to a redshift of 1.8. We will extend this previous work by considering a vacuum bubble embedded in a Tolman-Bondi space-time and looking at the coupled evolution of the bubble wall and the space-time metric. We will see how the expansion of the space in the interior of the bubble depends on the initial conditions of the bubble. We will also find the effects of the wall evolution on the Cosmic Microwave Background Radiation to determine what constraints, if any, the isotropy of the CMBR would place on the size of such a bubble and our location in it.
Mark Hartman with Cyrus Taylor
Using the AdSICFT Correspondence to
Predict Particle Masses in QCD
In the last two years, string theorists have been scrutinizing the implications of the so-called AdS/CFT (Anti deSitter space / conformal field theory) correspondence, one consequence of which is a duality between certain gauge theories in 4 dimensions and string theory (supergravity) on the space AdS^5 X S^5. This is a major step forward because it creates a relationship between the type of gauge theory that successfully describes electromagnetic, weak, and strong interactions, and the one force, gravity, that has failed to fit this general formula. A duality is defined as a one-to-one correspondence between quantities in the four-dimensional field theory and other quantities in the "stringy" picture of gravity. Exactly how deep this relationship extends is still unknown, but using this correspondence, one can gain insights into both of the theories on either side of the duality.
For example, in the AdS^5 X S^5 space, certain solutions of supergravity corresponding to the dynamics of a closed superstring yield discrete mass spectra that agree with the masses of glueballs. These particles, bound states of gluons (the particles that hold quarks together), are predicted by QCD, the 4-dimensional gauge theory that describes the strong interactions.
The first stage of this project is to complete an investigation which extends this line of thinking from the dynamics of closed strings to those of the simplest open strings in supergravity. It was thought the dynamics of this system would reproduce the mass spectrum for the lightest scalar and vector mesons: the pi and rho particles and their radial excitations. However, this prediction is not reproduced by the assumptions of our approach, but a clear statement of the AdS/CFT correspondence is revealed instead.
The second stage of this project involves taking a slightly different direction. The AdS/CFT correspondence is an example of the Holographic principle, according to which a quantum theory with gravity in d dimensions must be describable by a theory on its d-1
dimensional boundary. Either an extension of the first stage to include more complex particles or some other, closely-related aspect of the Holographic principle is to be investigated.
John Chunko with Tanmay Vachaspati
The determination of the presence of singularities in a general spacetime can be a very difficult task, especially since many apparent singularities can be removed by an appropriate coordinate transformation on the spacetime. One is therefore led to the construction of a set of rules that allow one to determine if non-coordinate singularities, namely, curvature singularities, are present in the spacetime under consideration. Such sets of rules are known as singularity theorems. These singularity theorems allow one to determine if actual singularities are present in a general spacetime if that spacetime satisfies certain energy and causal conditions.
The goals of this project will therefore be to study how these singularity theorems are constructed, as well as to apply them to specific spacetimes. To accomplish this goal we will have to examine how both timelike and null geodesics behave in curved spacetimes with specific requirements placed upon the curvature-inducing stress-energy tensor. We will then introduce the concept of causal structure and examine how this structure influences our previous results. We will then be able to formulate the singularity theorems for general spacetimes. Applications of these theorems to specific spacetimes will then be attempted.
Michael Boss with Kathy Kash
Photonic crystals are structures involving 2 or more media arranged in such a way as to have 1, 2 or 3 dimensional symmetry. Due to the different dielectric constants of the varying materials, photonic bandgaps can arise in the material. These bandgaps prohibit extended modes of photons in a certain frequency range. This can be exploited in devices in order to control the flow of light in a material. Photonic crystals can be used to make dielectric mirrors, resonant cavities, and waveguides - these represent just a few of their possible applications.
Using Maxwell's equations, photonic band gap structures can be modeled by a computer before actual fabrication. Given desired properties, a photonic crystal can be devised by computer, its modeled properties compared to those desired, and then fabricated. This project will focus on modeling 1-D, 2-D, and 3-D photonic crystals, and then actually fabricating the structures though techniques such as ultraviolet lithography. The properties of this construction will then be compared to those predicted by the computer model.
Elizabeth Hedrick with Glenn Starkman
Survey Strategies for Discovery of
Extrasolar Planets with a BOSS
The BOSS (Big Occulting Steerable Satellite) is a satellite designed to occult objects such as bright stars, in order to photograph the area around them. Among other uses, BOSS will be capable of revealing planets around other stars. This project will research the various phases of the expected planets, study planetary reflectivity as a function of the viewing angle, and work on an overall optimal survey strategy for extra solar planets.
Jeff Kolthammer with Robert Brown
Experimental Approach to Magnetic Field
Confinement in a Dual-strip System
There has appeared in literature a theoretical derivation of current conditions that lead to excellent magnetic-field confinement, called supershielding, in open-shield systems. A system consisting of two parallel, flat strips is used for illustration. We propose building a physical two-strip system and simulating the current densities derived for supershielding. The optimum magnetic-field confinement current conditions will be verified experimentally and numerically, and improving shielding beyond the derived conditions will be explored. Such an experiment will include the use of advanced electromagnetic calculations, various instrumentation and field measurements and sophisticated numerical methods.
Robert Kraig with Philip Taylor
A Kinetic Model of Phase Separation
Induced by Photo-polymerization
Using a molecular lattice to model a system of monomer and liquid crystal molecules, differential equations will be generated to describe the time behavior of the system when it is subjected to a light source With the incident light acting as a polymerizing agent, two processes must be accounted for in the equations: diffusion and polymerization. The differential equations for the time evolution of the local species concentrations will be numerically applied to the system, with the goal of providing insight into the microscopic nature of phase separation Results will be compared with experiment to determine whether the given model could adequately describe the phenomenon.
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