Undergraduate Honors Program - Physics and Astronomy Department
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The Honors Program requires a high level of accomplishment in a rigorous program of course work and culminates in research work which is presented as a senior thesis. Note particularly the requirements of independent study or thesis credit hours and the grade point average for a) all course work, b) course work in the major, and c) course work taken while a candidate for honors. Preparation during the junior year for the thesis project is strongly encouraged, but actual application for candidacy in the honors program usually is done promptly at the start of the senior year.
| Department Location: | 6301 Stevenson Center Vanderbilt University Nashville, TN 37240 |
| Mailing Address: | Vanderbilt University 6301 Stevenson Center VU Station B #351807 Nashville, TN 37235 |
| Phone: | 615-322-2828 |
| Fax: | 615-343-7263 |
| Email: | Physics-Astronomy@vanderbilt.edu |
| Website: | Department of Physics & Astronomy |
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Item Analytic Solutions of Two Electrons in Harmonic Confinement in an Optical Cavity(Vanderbilt University. Dept. of Physics and Astronomy, 2021-12) Huang, ChenhangThe possibility to control quantum systems with photons has stimulated recent interest in the study of quantum optical systems. While simple classical quantum systems admit well-known solutions, analysis of light-coupling quantum regimes remains lacking. In this work, we obtain analytic solutions for a light-coupling electron pair in harmonic confinement in a cavity by separating center-of-mass (CM) and relative motions. The CM part can be calculated in closed form or by exact diagonalization of the Hamiltonian, and the relative part is quasi-exactly solvable. We analyze the 2D results produced by the exact diagonalization method and reach conclusions on the effects of different system parameters. We also present 1D numerical simulations by Stochastic Variational Method (SVM) using Explicitly Correlated Gaussian (ECG) bases, which agree with our analysis in 2D. Our analytic solutions may provide a valuable calibration point for simulations in the quantum optical regime.Item An anomalous measurement of delta m31 squared from neutrino oscillations at the Daya Bay Reactor Neutrino Experiment(Vanderbilt University. Department of Physics and Astronomy, 2013-04-22) Burroughs, Hunter; Ernst, DavidIn 2012, the collaboration overseeing the Daya Bay Reactor Neutrino Experiment announced results which determined the magnitude of the mixing angle \theta_{13} with unprecedented precision. However, no attempt was made in the collaboration’s publications to predict the value of the most relevant mass-squared difference to the observed oscillation, \delta m^2_{31}. This paper presents the results of an analysis which suggests that the Daya Bay data prefers a value of \delta m^2_{31} which is far greater than its presently recognized value. Specifically, it is found that Daya Bay predicts \delta m^2_{31} = 3.53_(-1.07)^(+.74) × 10^(-3) eV^2, where the cited uncertainties correspond to the 99% confidence bounds. This measurement excludes the most precise current measurement of \delta m^2_{31}, the MINOS result, at a 99% confidence level and is in turn excluded by the MINOS data at a 10 \sigma level. The possibility that sterile neutrino effects are the cause of this anomalous result is considered and used to suggest further work.Item Axionlike Dark Energy and Particle Decay in theFuture of the Accelerating Universe(Vanderbilt University. Dept. of Physics and Astronomy, 2021-04-30) Norton, CameronThe 1998 discovery that the universe was accelerating in its expansion has yet to be explained theoretically, meriting the continual theoretical and observational study of this phenomena. In this thesis, we undergo a phenomenological study of the cosmological implications of this “dark energy” in two different ways. In the first part of this thesis, we examine the cosmological evolution of ultralight axionlike (ULA) scalar fields with potentials of the form V (φ) = m2f 2 [1 − cos (φ/f)]2 , with particular emphasis on the deviation in their behavior from the corresponding small-φ powerlaw approximations to these potentials: V (φ) ∝ φ 2n . We show that in the slow-roll regime, when φ˙2/2 V (φ), the full ULA potentials yield a more interesting range of possibilities for quintessence than do the corresponding power law approximations. For rapidly oscillating scalar fields, we derive the equation of state parameter and oscillation frequency for the ULA potentials and show how they deviate from the corresponding power-law values. We derive an analytic expression for the equation of state parameter that better approximates the ULA value than does the pure power-law approximation. In the second part, we study particle decay in the future of the accelerating universe. We generalize the result that in a cosmological constant dominated universe, the decay of matter into relativistic particles can never cause radiation to once again dominate over matter. We study both models of dark energy comprised of quintessence and cosmologies ending in a “big rip” in this context.Item Blazar Microvariations(Vanderbilt University. Dept. of Physics and Astronomy, 2009-04-20) Pittman, Cameron W.; Professor Robert KnopIn November 2006, the authors collected data on blazars PKS 0537-441, PKS 0447-439, and PKS 0208-5121 from the Cerra Tololo Inter-American Observatory in Chile. All three blazars are tested for microvariability, first by comparing relative magnitudes against unvarying stars, then through power spectrum analysis. The authors used GNU Scientific Library tools for the Fourier transforms needed for power spectrum analysis. Fourier transforms break down data into series of periodic functions. Running power spectra quantitatively illuminate periodicity and variability in data. The authors tested power spectra by using well-defined functions to better understand power spectra analysis. Through light curve analysis and power spectra analysis, the authors found PKS 0537-441 showed microvariability, PKS 0208-512 most likely did not show microvariability, and PKS 0447-439 did not show microvariability.Item DARK MATTER MAY NOT BE SO DARK: Testing Massive Primordial Black Hole Dark Matter with Galactic X-Ray Emission(Vanderbilt University. Dept. of Physics and Astronomy, 2024-04-16) McPhaul, NolanWere primordial black holes (PBHs) to exist, they could constitute a significant portion of dark matter in our universe which could be explored through gravitational wave emission, gravitational lensing, and electromagnetic observations. Assuming PBHs as a dark matter candidate, we determine the X-ray emission they would radiate from accreting gas in their host galaxy by modeling the dark matter particles in the Romulus25 cosmological simulation as clusters of PBHs. Upon simulating such emission, we compare our X-Ray luminosity functions to those derived from observations with the Chandra X-Ray Telescope to constrain the abundance of PBHs compared to dark matter as a function of PBH mass spanning 10^-2 − 10^5 M . Our results highly constrain the most massive PBHs but leave a vast sea of stellar and sub-stellar mass PBHs unscathed by falling under the flux limitations of Chandra. Therefore, further studies are needed in such a mass regime to explore the possibility of PBHs as a considerable source of dark matter and black holes in our universe. The implications of such could have drastic impacts on our understanding of the composition, machinations, and evolution of our universe.Item Dark radiation from particle decays during big bang nucleosynthesis(Vanderbilt University. Dept. of Physics and Astronomy, 2012-04) Menestrina, Justin; Scherrer, Robert J. (Robert Joseph), 1959-Cosmic microwave background (CMB) observations suggest the possibility of an extra dark radiation component, while the current evidence from big bang nucleosynthesis (BBN) is more ambiguous. Dark radiation from a decaying particle can affect these two processes differently. Early decays add an additional radiation component to both the CMB and BBN, while late decays can alter the radiation content seen in the CMB while having a negligible effect on BBN. Here we quantify this difference and explore the intermediate regime by examining particles decaying during BBN, i.e., particle lifetimes τ_X satisfying 0.1 sec < τ_X < 1000 sec. We calculate the change in the effective number of neutrino species, Neff, as measured by the CMB, ΔN_CMB, and the change in the effective number of neutrino species as measured by BBN, ΔN_BBN, as a function of the decaying particle initial energy density and lifetime, where DNBBN is defined in terms of the number of additional two-component neutrinos needed to produce the same change in the primordial 4He abundance as our decaying particle. As expected, for short lifetimes (τ_X < 0.1 sec), the particles decay before the onset of BBN, and DNCMB = DNBBN, while for long lifetimes (τ_X >1000 sec), ΔN_BBN is dominated by the energy density of the nonrelativistic particles before they decay, so that ΔN_BBN remains nonzero and becomes independent of the particle lifetime. By varying both the particle energy density and lifetime, one can obtain any desired combination of N_BBN and ΔN_CMB, subject to the constraint that DNCMB N_BBN. We present limits on the decaying particle parameters derived from observational constraints on ΔN_CMB, and N_BBN.Item The Data Acquisition and Calibration of Luminosity at the Compact Muon Solenoid Experiment(Vanderbilt University. Dept. of Physics and Astronomy, 2024) Tang, JessicaItem Data Logistics and the CMS Analysis Model(Vanderbilt University. Dept. of Physics and Astronomy, 2009-04-20) Managan, Julie E.The Compact Muon Solenoid Experiment (CMS) at the Large Hadron Collider (LHC) at CERN has brilliant prospects for uncovering new information about the physical structure of our universe. Soon physicists around the world will participate together in analyzing CMS data in search of new physics phenomena and the Higgs Boson. However, they face a significant problem: with 5 Petabytes of data needing distribution each year, how will physicists get the data they need? How and where will they be able to analyze it? Computing resources and scientists are scattered around the world, while CMS data exists in localized chunks. The CMS computing model only allows analysis of locally stored data, "tethering" analysis to storage. The Vanderbilt CMS team is actively working to solve this problem with the Research and Education Data Depot Network (REDDnet), a program run by Vanderbilt's Advanced Computing Center for Research and Education (ACCRE). I participated in this effort by testing data transfers into REDDnet via the gridFTP server, a File Transfer Protocol which incorporates an LHC Computing Grid security layer. I created a test suite which helped identify and solve a large number of problems with gridFTP. Once optimized, I achieved sustained throughputs of 700-800 Megabits per second (Mbps) over a 1 Gigabit per second (Gbps) connection, with remarkably few failures. GridFTP is the gateway between REDDnet and CMS, and my tests were designed to exercise and harden this important tool. My results support other indications that the REDDnet system will be a successful solution to the limitations of data-tethering in the CMS computing model.Item Deformed Explicitly Correlated Gaussians(Vanderbilt University. Dept. of Physics and Astronomy, 2022-12) Beutel, MatthewStrong coupling of cavity electromagnetic modes and molecules has emerged as an area of intense theoretical and experimental interest. Such systems are of particular interest due to their ability to modify the physical and chemical properties of materials. In this work, I use a stochastic variational method (SVM) to construct optimized light-matter coupled wave function. By using SVMs to select the best basis states, we are able to achieve highly accurate energies and wave functions. In this work, I will be solving for the Pauli-Fierz (PF) nonrelativistic QED Hamiltonian. In this work I will introduce a new basis type Deformed Explicitly Correlated Gaussians (DECGs). DECGs are a modified form of explicitly correlated Gaussians (ECGs) where the basis is chosen such that the dipole self-interaction term can be eliminated. These calculations will be compared to those performed with traditional ECGs, demonstrating their superiority in cases where a non-spherical potential exists, such as the dipole self-interaction term.Item Density profiles of dark matter halos(Vanderbilt University. Dept. of Physics and Astronomy, 2010-04) Robbins, Katherine; Berlind, Andreas A., 1972-Item Developing High-Brightness Electron Beam Sources for Producing Quantum Degenerate Electron Beams(Vanderbilt University. Dept. of Physics and Astronomy, 2011-04) Kohler, Jonathan; Brau, Charles A., 1938-The Pauli Exclusion Principle places a fundamental limit on the brightness of an electron beam. Developing a cathode which can reach this limit is useful for achieving maximum operation in current applications of electron beams, but also opens new areas of physics to be explored. When the phase space of the electron beam is filled to the maximum density, the electrons will experience a degeneracy pressure, similar to that which keeps a neutron star from collapsing. One promising source for a quantum degenerate beam is field emission from adsorbates on carbon nanotubes. Adsorbates have been shown to provide several orders of magnitude enhancement to emission brightness, which approaches the degeneracy limit. We have developed experiments to test various adsorbates, in order to find those which bind tightest and provide the largest enhancement in brightness. Continuing work to discover better adsorbates should soon allow for the generation of a quantum degenerate electron beam.Item The distribution of ejected stars around a super massive black hole binary due to three-body scattering(Vanderbilt University. Dept. of Physics and Astronomy, 2010-04) Benson, Amanda; Holley-Bockelmann, KellyItem Emittance and entropy of electron beams(Vanderbilt University. Department of Physics and Astronomy, 2014-04) Erickson, Collin; Brau, Charles A., 1938-Creating high-brightness electron beams, which have many practical applications, is done with cathodes in regions with large electric field by field emission. The brightness is high when the current is high and the volume of the beam in phase space is small. An estimate of the phase space volume is the rms emittance. The simulations described in this report show that the beam emitted by a gated diamond field emitter of the type fabricated at Vanderbilt has an exquisitely small emittance, on the order of a few nm. This is probably too small to measure. The rms emittance is generally thought to be constant for a beam or increasing in the presence of aberrations in the beam optics, but simulations show that this is not true. The rms emittance rises and falls according to the geometry that surrounds the beam. The entropy of an electron beam can be calculated, and should be constant if done in six dimensional phase space, and approximately constant in four dimensions. Calculations show that the entropy is not constant in two nor four dimensions. Rather, the entropy changes over time with a shape similar to how the emittance changes, which includes a local maxima at the entrance to an aperture and minima on either side. It is not clear if the fault is with the calculations or theory. To our knowledge, this is the first time that the entropy of a particle beam has been computed and used in a quantitative fashion. Future research should explore the applications and limitations of this concept.Item Engineering a perfusion-enabled mechanical compressor for long-duration immobilization and microscopy of cells and small organisms(Vanderbilt University. Dept. of Physics and Astronomy, 2011-04) Jiang, Liwei; Janetopoulos, ChristopherThe study of living specimens is essential to the understanding of organismal behavior. Unfortunately, a major difficulty in the study of live organisms is that many move in and out of the field of view or focal plane during microscopy. The present work seeks to combat this considerable problem by developing a mechanical microcompressor that immobilizes living cells and small organisms for long-duration optical microscopy. The device, dubbed the "Commodore Compressor," features two key innovations: (1) the integration of a perfusion system to keep the trapped specimen alive over several hours, as well as permitting the addition of chemoattractants, drugs, and other chemicals; (2) the incorporation of an optional patterned PDMS platform to improve the efficacy of immobilization in a targeted, organism-specific manner. One application of the Commodore Compressor is in monitoring the change in protein bioluminescence intensity in many trapped Saccharomyces cerevisiae cells during synchronized cell cycles. The experiment's feasibility and key techniques have been well demonstrated, although bioluminescence cannot currently be visualized. A second application involves fluorescence imaging of the neural network development of immobilized Caenorhabditis elegans over many hours. The development of new patterned PDMS platform designs, aided by the innovative use of established techniques, has driven the present work toward accomplishing the goal, but true long-term viability remains elusive. The Commodore Compressor may be directly used or easily adapted for many other specimen types and experimental scenarios.Item Expected Host Galaxy Properties of PTA Detectable Massive Black Hole Binaries(Vanderbilt University. Dept. of Physics and Astronomy, 2021-12-06) Cella, KatharineMassive black hole binaries (MBHB) produce gravitational waves (GW) that will be detectable with pulsar timing arrays within the next few years. We determine the properties of the host galaxies of MBHB at the time they are producing detectable GW. The population of MBHB systems we evaluate is from the Illustris cosmological simulations taken in tandem with post processing semi-analytic models of environmental factors in the evolution of binaries. Upon evolving to the frequency regime detectable by pulsar timing arrays, we calculate the detection probability of each system using a variety of different values for red and white noise. We average over multiple realizations of the universe by re-sampling the host galaxy properties using a kernel density estimator to approximate the statistical distributions of the universe. Excitingly, we find that detectable systems have host galaxies that are clearly distinct from the overall population. With conservative noise factors, we found that stellar metallicity, for example, peaks at approximately twice solar metallicity as opposed to the total population of galaxies which peaks at approximately solar metallicity. Additionally, the most detectable systems are brighter and more red in color than the overall population. These results can be used to develop effective search strategies for identifying host galaxies and electromagnetic counterparts following GW detections.Item Exploring the Local Association : a nearby, young kinematic stream of stars in the solar neighborhood(Vanderbilt University. Dept. of Physics & Astronomy, 2008) Saling, Chris; James, David J.During the course of my Honors Research Project, I worked with Dr. David James to determine whether a group of target stars are members of the Local Association. I did this by reducing spectroscopic data, taken by Dr. James, in order to determine the radial velocity and lithium contents of the stars. Using the radial velocity measurements, the kinematics of each star was then defined by determining their U,V,W space motions. Lithium measurements were used to establish star youth and provide further evidence to support membership of the Local Association.Item Finite-Element Analysis of Low-Power Laser Heating in Gold::Vanadium Dioxide Nanocomposites(Vanderbilt University. Dept. of Physics and Astronomy, 2011-04) MacQuarrie, Evan; Haglund, Richard F., Jr., 1942-Finite element modeling was performed using COMSOL Multiphysics to study the thermal dynamics of gold::vanadium dioxide (VO$_{2}$) nanocomposites. These simulations were done to understand the data from transient absorption pump probe measurements taken over the previous two years by the author. The various parameters contributing to the dynamics of the system were systematically varied within the simulation in order to understand how the various properties of the nanocomposite affect the thermodynamics of the system. It was determined that the background temperature and the optical properties of the film make the dominant contributions to the system response. The simulation was able to predict the maximum change in transmission measured in experiment fairly well but could not predict the speed at which the system responded to the pump laser. Steps to improve upon the agreement between experiment and simulation are proposed.Item First observation of the direct detection of positive D-meson into anti-K-long + 3 pions and negative D-meson into K-long + 3 pions with the Fermilab FOCUS experiment(Vanderbilt University. Department of Physics and Astronomy, 2014-04) Stewart, Cameron; Johns, Will E.In this thesis the decays of positive D-mesons into neutral anti-K-mesons and three charged pions and of negative D-mesons into neutral K-mesons and three charged pions are reconstructed in both long and short neutral K-meson states. The data were taken with the Fermilab FOCUS spectrometer. This constitutes the first observation of these decays in the long K-meson mode. We detail the cuts necessary to find the branching ratio for the K-long to K-short modes for both positive and negative D-mesons, show that the ratio is 0.89, and detail further work that remains to be done. The K-long mode is reconstructed using the D-meson flight direction, the direction of the charged pions, and the energy deposited in the hadron calorimeter. The K-short decay is reconstructed directly using tracking information in the pi plus - pi minus decay mode.Item First-Principles Calculations of Electronic and Vibrational Properties in Semiconductors(Vanderbilt University. Dept. of Physics and Astronomy, 2025-04-23) Demos Negash; Professor Sokrates Pantelides, Ph.D.Item Fragmentation in Coulomb Explosion of Hydrocarbons(Vanderbilt University. Dept. of Physics and Astronomy, 2024-12-02) Samuel S. Taylor; Professor Kalman VargaFragmentation dynamics in the Coulomb explosion of hydrocarbons—specifically methane, ethane, propane, and butane—are investigated using time-dependent density functional theory (TDDFT) simulations. The goal of this work is to elucidate the distribution of fragments generated under laser-driven Coulomb explosion conditions. A detailed analysis reveals the types of fragments formed, their respective charge states, and the optimal laser intensities required to achieve various fragmentation pathways. The results indicate distinct fragmentation patterns for each hydrocarbon, which correlate with differences in molecular structure and ionization potential. Additionally, the laser parameters that maximize fragmentation efficiency are identified, offering valuable insights for guiding experimental setups. This research advances our understanding of Coulomb explosion mechanisms and provides a foundation for further studies on controlled molecular fragmentation.
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