Bulletin of the American Physical Society
2020 Annual Meeting of the Far West Section
Volume 65, Number 17
Friday–Saturday, October 9–10, 2020; Virtual, Pacific Time
Session L01: Astrophysics, Gravitation, Nuclear Physics, and OtherLive
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Chair: Philip von Doetinchem, University of Hawaii at Manoa |
Saturday, October 10, 2020 2:00PM - 2:12PM Live |
L01.00001: Analyzing an Unusual Population of Weak CN Stars in the Disk of the Andromeda Galaxy (M31) Arya Maheshwari, Alexandra Masegian, Puragra Guhathakurta, Amanda Quirk, Rachel Raikar, Caelum Rodriguez, Antara Bhattacharya, Anika Kamath The recent discovery of a population of “weak CN” AGB stars in the disk of the Andromeda Galaxy (M31) has raised new questions about how massive stars evolve. This population is characterized by its unconventional mix of carbon- and oxygen-based spectral features, the most prominent of which is a weak double-peaked CN absorption line at around 8000 Angstrom. We present a sample of these weak CN stars identified from an analysis of the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) and the Panchromatic Hubble Andromeda Treasury (PHAT) surveys. Our sample was constructed via an automated classification algorithm that compared candidate stars to coadded spectral templates of visually-identified weak CN and carbon stars. Each star was assigned a score based on this comparison, quantifying its similarity to a weak CN model population. Results from this spectroscopic pipeline and analysis of candidate stars in color-magnitude space, as well as comparisons to stellar track models, suggest that weak CN stars may represent a phase of stellar evolution that is entirely distinct from the carbon-rich phase previously studied in AGB stars. We propose that further investigation into these unusual stars could lead to a better understanding of massive evolved stars. [Preview Abstract] |
Saturday, October 10, 2020 2:12PM - 2:24PM Live |
L01.00002: Gamma Ray Analysis of the Most Energetic Blazars to Probe the Cosmos Yashika Batra, Jewon Im, Nathan Nguyen Proper measurements of the Extragalactic Background Light (EBL), the radiation field of all infrared to light emitted in the Universe since reionization, are key to understanding the cosmic makeup and evolution of the universe. However, its direct measurement is difficult due to bright foreground emissions. An alternative method is to indirectly probe the EBL from its interaction with gamma rays emitted by blazars. The Fermi-LAT and H.E.S.S collaborations proposed using a scaling factor alpha to normalize EBL density based on a previously existing model. However, numerous “problematic” sources that deviate more than a discrepancy of 3 sigma from an EBL model were present in Fermi-LAT’s 4FGL-DR2 catalog, which contained 10 years of data. We performed a new gamma ray analysis on 12 years of Fermi-LAT observations, focusing on “problematic” and bright sources. The changes on the scaling factor alpha derived from our analysis resolve the issue for most of the “problematic sources”, while creating a new outlier from our “bright sources” sample. By estimating the factor alpha for a large number of blazars observed by the Fermi Large Area Telescope (Fermi-LAT), this study will contribute to the creation of a map of the density of the EBL. [Preview Abstract] |
Saturday, October 10, 2020 2:24PM - 2:36PM Live |
L01.00003: On the Role of Einstein-Cartan Gravity in Fundamental Particle Physics Carl Diether, Joy Christian Two of the major open questions in particle physics are: (1) Why are the elementary fermionic particles that are so far observed have such low mass-energy compared to the Planck energy scale? And (2), what mechanical energy may be counterbalancing the divergent electrostatic and strong force energies of point-like charged fermions in the vicinity of the Planck scale? In this paper, using a hitherto unrecognized mechanism derived from the non-linear amelioration of Dirac equation known as the Hehl-Datta equation within Einstein-Cartan-Sciama-Kibble (ECSK) extension of general relativity, we present detailed numerical estimates suggesting that the mechanical energy arising from the gravitationally coupled self-interaction in the ECSK theory can address both of these questions in tandem. [Preview Abstract] |
Saturday, October 10, 2020 2:36PM - 2:48PM Live |
L01.00004: Current Advancements on Short-range Tests of Gravity at Humboldt State University Emily Ord, Kyle Galaz, Michael Gengo, Alyssa Johnson, Frank Trombetta, Kassandra Weber, C.D. Hoyle As a result of discrepancies between the Standard Model and General Relativity, gravitational experiments have remained at the forefront of experimental physics research in an effort to unify these models. Theories which attempt this unification often include features that violate the Weak Equivalence Principle (WEP) and/or the gravitational Inverse-Square Law (ISL), potentially bringing our fundamental understanding of gravity into question. Therefore, students, faculty and Humboldt State University have constructed an apparatus that will measure the effects of gravity at a submillimeter scale. This experiment measures the twist of a torsion pendulum as an attractor mass is oscillated nearby, providing a time-varying torque on the pendulum. In the experiment, the size and distance dependence of the torque are measured, thereby providing means to determine deviations from accepted models of gravity on untested distance scales. This talk will focus on the new features implemented in our data analysis of the motion of the pendulum. In addition, we will provide updates on the project and how the lab has adjusted to research under the Covid-19 pandemic restrictions. [Preview Abstract] |
Saturday, October 10, 2020 2:48PM - 3:00PM Live |
L01.00005: Combining State-of-Art Nuclear Structure Theory with Modern Reaction Descriptions: Nucleon-Induced Reactions Emanuel Chimanski, Jutta Escher, Walid Younes Nucleon-induced reactions have been used to determine nuclear structure properties and indirect information on nuclear reaction cross sections. Nucleosynthesis as well as modern medical applications rely on capture and inelastic-scattering cross section information that are difficult and sometimes impossible to obtain experimentally. Therefore, theoretical models are required to supplement or directly provide the necessary information. Current reactions calculations rely on simplified models, commonly developed for spherical targets, with limited precision and predictability. In reality, most nuclei of interest are deformed and the complexity of such systems challenges the standard models available. To improve the predictive power of nuclear-reaction calculations, we are combining a state-of-the-art nuclear structure approach with a modern reaction description. Specifically, we are extending the transition density formalism to include reactions with deformed targets. Nuclear excitations are described within a deformed QRPA framework and angular momentum restoration techniques are applied. Our objective is to obtain transition potentials for different exited states and we will present the preliminary results for representative cases. [Preview Abstract] |
Saturday, October 10, 2020 3:00PM - 3:12PM Live |
L01.00006: Causal Intuition and Delayed-Choice Experiments Michael Heaney This paper proposes a resolution of the delayed-choice paradox of the Conventional Theory of quantum mechanics, where a particle seems to know what will happen in the future, and changes its present behavior accordingly. A comparison of the Conventional Theory with an Advanced Theory and a Symmetrical Theory of the same gedankenexperiment suggests that the apparent paradox is caused by an incorrect assumption about the interaction of a wavefunction with a beam-splitter. Once this assumption is corrected, there is no paradox in any of these three theories. [Preview Abstract] |
Saturday, October 10, 2020 3:12PM - 3:24PM Live |
L01.00007: HALO7D Extension Survey: Analysis of Keck DEIMOS Spectra and Velocities of Milky Way Halo Stars in the COSMOS Field Esha Umbarkar, Ryan Cho, Puragra Guhathakurta, Kevin McKinnon, Constance Rockosi, Miranda Apfel The stellar halo of the Milky Way (MW), an extended sparse component that surrounds the main disk, is composed mostly of old stars and contains vital clues about the MW’s cannibalism history. In this research project, we analyzed DEIMOS multislit spectra of stars in the COSMOS field from the HALO7D survey, a multidimensional HST+Gaia+Keck study of the MW halo. Based on the known Gaia-based apparent magnitudes of the target stars, we calibrated the spectra slitmask by slitmask. This process allows us to explore the effects of the Earth’s atmosphere and the DEIMOS spectrograph on the spectra. We present the line-of-sight velocity distributions of the stars, categorized in two ways: (1) spectral type, and (2) color-magnitude diagram. We compared our data to the prediction of the Besançon model, a simple smooth analytical model of the MW. The model stars were grouped in the same two ways as the data. There is generally good agreement between the data and the Besançon thin and thick disk predictions, but, as has previously been noted, the Besançon halo density profile is shallower than observed. These kinds of data and model comparisons provide insight into the structure and substructure (departure from smoothness) of the MW, revealing information about its accretion history. [Preview Abstract] |
Saturday, October 10, 2020 3:24PM - 3:36PM Live |
L01.00008: Toward the Next Generation of Optical-Model Potentials Cole Pruitt, Jutta Escher, Mack Atkinson, Wim Dickhoff, Lee Sobotka, Bob Charity Almost 70 years after their debut, phenomenological optical-model potentials (OMPs) remain the standard for theoretical descriptions of low-energy nuclear reactions. A handful of venerable nucleon-nucleus potentials, including Koning-Delaroche and Chapel Hill ‘89, accurately reproduce average scattering observables on stable, near-spherical isotopes up to several hundred MeV. But despite caveats from their creators, these potentials are often pushed beyond their intended limits to make predictions for highly-deformed, highly-asymmetric systems, many of which will be newly accessible in the FRIB era. Are these extrapolations justifiable, or do they yield unreliable predictions? Are there sufficient experimental structure and scattering data to constrain the functional forms of the potential? To address these questions, we have begun to characterize the inherent uncertainty in widely-used OMPs and to study the sensitivity of the potentials’ components to various sectors of experimental data. We compare standard phenomenological potentials with new dispersive and microscopic optical models and formulate recommendations for developing the next generation of OMPs. [Preview Abstract] |
Saturday, October 10, 2020 3:36PM - 3:48PM Live |
L01.00009: Measurement of the expected 57 keV neutron anti-resonance in $^{40}$ Ar using a time of flight neutron beam Tyler Erjavec A measurement of the transmission coefficient for neutrons through a thick ($\sim$3 atoms/b) natural liquid argon target in the energy range 40-70 keV has been performed by the Argon Resonance Transmission Interaction experiment (ARTIE) using a time of flight neutron beam at Los Alamos National Laboratory (LANL). In this energy range theory predicts an anti-resonance in the $^{40}$Ar cross section near $57$ keV, but the existing data, coming from an experiment performed in the 90s (Winters. et al.), do not support this. The goal of ARTIE is to resolve this disagreement by improving knowledge of neutron transport in argon. This measurement is crucial for the Deep Underground Neutrino Experiment (DUNE) because it provides a viable means of calibration via a Pulsed Neutron Source (PNS), and allows a deeper understanding of signals and backgrounds for the low energy science program. [Preview Abstract] |
Saturday, October 10, 2020 3:48PM - 4:00PM |
L01.00010: Modelling and Analysis of Synthetic Jet Actuators: Multiphysics versus Analytical Baris Gungordu, Mark Jabbal, Atanas Popov This study concentrates on the modelling of piezoelectrical-diaphragm driven synthetic jet actuator. Two different models, analytical and CFD-type Multiphysics, were studied and then compared against two sets of in-house experimental data for their jet velocity one for opposite diaphragm-orifice configuration and the other for adjacent diaphragm-orifice configuration. Overall, both models have successfully predicted the shape of the velocity response. The Multiphysics simulation has estimated the peak jet velocity with a difference of 0.3 m/s and 0.8 m/s for Case 1 and 2, respectively. The analytical model has estimated the resonant frequency with a shift of 100 Hz for both cases. There is a difference in the peak jet velocity of 2.9 m/s and 1.2 m/s at the mechanical resonance for Case 1 and 2, respectively. Multiphysics simulation has the advantage of flow visualization including vortex formations and in-detailed flow physics investigation such as formation criterion and Stroke length. The analytical model has the advantage of producing fast results to give an idea of the expected jet velocity scale with a limited number of parameters.~ [Preview Abstract] |
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