Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 62, Number 17
Friday–Saturday, October 20–21, 2017; Fort Collins, CO
Session L4: Gravitation and Cosmology |
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Chair: Cynthia Galovich, University of Northern Colorado Room: Lory Student Center 304 |
Saturday, October 21, 2017 11:10AM - 11:34AM |
L4.00001: Remnant Echoes: Mapping the Cosmos via Large Spectroscopic Surveys Invited Speaker: Adam Myers One of the major unsolved mysteries in physics is the nature of cosmic acceleration---the onset of an increased rate of expansion for our Universe about 6.5 billion years ago. Probing this cosmic acceleration or ``dark energy'' requires an understanding of how distances in the Universe change with time, or, in other words, constraints on the evolution of the cosmological distance-redshift relation. Redshifts are relatively straightforward to measure via large spectroscopic surveys of the sky. Distances are trickier to ascertain, however. One technique is to use the observed flux from objects of known brightness (``standard candles'') in order to determine their luminosity distance. This approach, using supernovae as the standard candles, led to the first confirmation of cosmic acceleration and earned the 2011 Nobel Prize in Physics. A different but complementary approach is to use the angle subtended by tracers of known physical size in order to measure their angular diameter distances (a ``standard ruler'' test). Such a standard ruler, a remnant of a primordial ``Baryon Acoustic Oscillation'' (or BAO) is present on scales of $\sim$150 Mpc in maps of tracers of large scale structure in the Universe such as galaxies and quasars. Large spectroscopic surveys of the sky have thus emerged as a promising approach with which to constrain the acceleration of our Universe, through measurements of the apparent scale of the BAO. I will discuss my collaborative work producing extensive 3-D maps of our Universe with the Sloan Digital Sky Survey (SDSS) Baryon Oscillation Spectroscopic Surveys (BOSS and eBOSS) in order to constrain the evolution of the scale of the BAO feature. I will also outline my current efforts as part of the Dark Energy Spectroscopic Instrument (DESI) collaboration's Data Systems team. The DESI survey is an upcoming Stage IV dark energy experiment that will target over 30 million galaxies and about 2.5 million quasars in order to measure the evolution of the BAO scale throughout cosmic history. [Preview Abstract] |
Saturday, October 21, 2017 11:34AM - 11:46AM |
L4.00002: Thermodynamic Studies of Phase Transitions in Inflationary Cosmology Kendall Mallory I will describe some thermodynamic studies of cosmological phase transitions to inflationary spacetime modes. We employ averaging methods assuming some kind of thermodynamic equilibrium is represented by these states. Some results are presented from direct partition sum solutions over normal modes in a scalar inflaton field, and also from metropolis Monte-Carlo simulations utilizing a scaling random walk method designed to avoid stiffness in the averaging near transitions. [Preview Abstract] |
Saturday, October 21, 2017 11:46AM - 11:58AM |
L4.00003: Holographic Entanglement Entropy in Higher Dimensions Zachary Polonsky Maldacena’s AdS/CFT conjecture gives strong evidence for the holographic nature of gravity and provides insight into the relationship between gravitational theories in $(D+1)$-dimensions and non-gravitational theories in $D$-dimensions. The reflection in the gravitational theory of quantum entanglement in the non-gravitational CFT was only understood in a very limited context until the holographic entanglement entropy (HEE) result of Ryu-Takayanagi (and its covariant generalization due to Hubeny-Rangamani-Takayanagi) provided considerable insight into the role that entanglement plays in Maldacena’s duality. Tests of this result have been largely limited to the technically simple setting of 2+1-dimensional gravity which exhibits no local degrees of freedom, and to systems with obvious thermal interpretations. The purpose of this work is to further explore the HEE result in higher dimensional contexts as well as for systems with less obvious thermal interpretations. We consider both standard Schwarzchild-type black holes as well as the topological black holes of the BTZ-type. This work will provide further support for the HEE result and may very well provide insight into our understanding of how sensitive gravitation is to differences in dimension. [Preview Abstract] |
Saturday, October 21, 2017 11:58AM - 12:10PM |
L4.00004: Symmetries of Geodesics for Homogeneous Gravitational Fields David Maughan, Charles Torre In Einstein's general theory of relativity freely falling test particles follow geodesics of the spacetime geometry. Some geodesics have symmetries, known as affine collineations. Mathematically, these affine collineations are transformations that preserve the connection defined by the metric, without preserving the metric. Physically, they change the notion of lengths and angles, while preserving the notion of parallelism. Associated with each affine collineation are two conserved quantities. Previously these quantities were understood to be non-Noetherian, however we show that they can be derived from a direct application of Noether's theorem. We calculate all affine collineations and their corresponding conservation laws for all of the homogeneous solutions to the Einstein Field Equations in vacuum, with perfect fluid sources, and with homogeneous electromagnetic sources. [Preview Abstract] |
Saturday, October 21, 2017 12:10PM - 12:22PM |
L4.00005: The Characteristic Problem in General Relativistic Magnetohydrodynamics Ryan Hatch We consider the characteristic problem in relativistic ideal magnetohydrodynamics. We discuss the structure, formulation, and simplifications of the relevant equations in 3+1 dimensions. Having formulated the equations in balance law form, we find the characteristic equation and discuss the resultant wave speeds. We complete the diagonalization process by finding the left and right eigenvectors. The latter will have applicability in computational work in general relativistic magnetohydrodynamics (GRMHD). Indeed, finding these eigenvectors allows for the application of certain high resolution shock capturing techniques. In particular, the types of problems we are interested in include the dynamics of strongly magnetized neutron stars and their magnetospheres. [Preview Abstract] |
Saturday, October 21, 2017 12:22PM - 12:34PM |
L4.00006: An Undergraduate Test of Gravitational Time Dilation Brian Patterson, M. Alina Gearba, Jerry S. Sell, Mario Serna, M. Shane Burns, Michael D. Leveille, Jeffrey Steele Students at Colorado College and cadets at the US Air Force Academy have conducted an experimental test of gravitational time dilation. This relativistic effect, highlighted in the movie \textit{Interstellar}, causes clocks to tick more slowly near massive objects. A terrestrial measurement of gravitational time dilation was made by comparing signals generated by a GPS frequency standard, which is based on sea-level time, to a cesium-beam frequency standard located at several different elevations across Colorado. The effect is small but observable; for the highest elevation studied (4302 m on the summit of Pikes Peak), a local clock ticks only 41 ns/day faster than a clock at sea level. Our results are consistent with the predictions of general relativity to within the experimental uncertainty. We briefly discuss implications of gravitational time dilation for GPS operations, since the GPS would be useless if time dilation effects are not compensated. This work was supported by grants from the Mellon Foundation fostering civilian/military collaboration. [Preview Abstract] |
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