Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session D16: Tests of General Relativity I |
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Sponsoring Units: DGRAV Chair: Scott Ranson, University of Virginia Room: Sheraton Grand Ballroom I |
Saturday, April 13, 2019 3:30PM - 3:42PM |
D16.00001: A New Multi-mode Apparatus to Determine G Charles D Hoyle, Ricardo Santiago Decca, Stefan W Ballmer Of all the fundamental constants in nature, G, the Newtonian gravitational constant, is known with the least precision. The world's best experiments yield values which are incompatible with one another and differ by about 50 times the uncertainty of the most precise experiment. Two recent experiments have, however, obtained consistent results at the 12 ppm level. Since it is possible that a portion of the past discrepancies between determinations of G can be traced back to the methodology used, the research group at IUPUI, in collaboration with Humboldt State University and Syracuse University, will combine different approaches to determine G within the same torsion pendulum apparatus. We expect to obtain a measurement of G at the 2 ppm level from each method. With the experiments carried out in the same apparatus, the effort will also help to understand the current discrepancies among existing experimental results. This talk will explore the experimental configurations as well as give a general status update on this relatively new project. | |
Saturday, April 13, 2019 3:42PM - 3:54PM |
D16.00002: Improving Short Range Gravity Limits With Cylinders Thomas Bsaibes, Luis Pires, David Czaplewski, Daniel Lopez, Ricardo Santiago Decca Some unification theories and extensions to the standard model predict a non-Newtonian interaction between two point masses separated by distance r. In both cases the interaction is Yukawa-like, V(r) = αe^{-r/λ}/r, with strength α and characteristic length λ. At separations below 1 μm the parameters that characterize the interaction are poorly bounded. Previous experiments have used a spherical test mass in front of a plane to place upper bound limits on the interaction strength. Our estimates show that cylindrical test masses will reduce upper bounds by ∼2 orders of magnitude. To this end a system implementing a cylindrical test mass is under development. The cylinders will be 500 μm long with radius of 150 µm. They will be created using maskless grayscale lithography techniques to place them directly onto a high-Q oscillator. The success of future measurements, however, depends on the ability to align the cylinder's longitudinal axis perpendicular to the normal of the plane. We are developing a scheme that uses capacitance to align the cylinder-plane system and determine their separation. A scaled up version of our system has been constructed to verify if capacitance is a viable indicator of alignment and separation. The results will be compared to COMSOL simulations. | |
Saturday, April 13, 2019 3:54PM - 4:06PM |
D16.00003: Tests of General Relativity with the Binary Black Hole Signals from the LIGO-Virgo Catalog GWTC-1 Nathan K Johnson-McDaniel The observations of binary black hole coalescences by Advanced LIGO and Advanced Virgo offer unprecedented opportunities for testing the predictions of general relativity for the gravitational waveforms from these highly dynamical, strong-field events. We apply four types of tests of general relativity to the ten highly significant binary black hole detections in the catalog GWTC-1. In one test, we subtract the best-fit waveform and check the consistency of the residuals with detector noise. In the second test, we check the consistency of the low- and high-frequency portions of the signals. The third test introduces phenomenological deviations in the waveform model (including in the post-Newtonian coefficients) and checks that they are consistent with zero. The fourth test constrains modifications to the propagation of gravitational waves due to a modified dispersion relation, including that from a massive graviton. We present results for individual events as well as combined results using the most significant events. Additionally, for strong events observed by all three detectors, we compare the evidence for purely tensor polarizations to that for purely non-tensor polarizations. | |
Saturday, April 13, 2019 4:06PM - 4:18PM |
D16.00004: Testing Gravity Below 50 micrometers John G Lee, Svenja Fleischer, H Erik Swanson, Eric G Adelberger, Blayne R Heckel Searches for violations of the gravitational inverse square law at small separations constrain proposed phenomena such as large extra spatial dimensions and the chameleon mechanism. Our Fourier-Bessel torsion-pendulum measures gravitational torques on test masses with 18-fold and 120-fold symmetric wedge patterns cut from 50µm thick platinum foils. The total masses of the 120-fold patterns are only 0.6 g, but yield highly resolved signals. I will present preliminary results obtained at separations between 5 mm and 50 µm. | |
Saturday, April 13, 2019 4:18PM - 4:30PM |
D16.00005: Optimizing LIGO with LISA forewarnings to improve black-hole spectroscopy Rhondale Tso, Davide Gerosa, Yanbei Chen
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Saturday, April 13, 2019 4:30PM - 4:42PM |
D16.00006: Progress on Short-range Tests of Gravity at Humboldt State University Jackson G Stillman, Nicholas Hernandez, Kassandra Weber, Berlin A Del Aguila, Charles D Hoyle Of the four fundamental forces, gravity is the only one that does not have a suitable quantum-mechanical description. General Relativity, which embodies our current understanding of gravity, is separate from the Standard Model that explains the other three fundamental forces. Theories which attempt to unify the Standard Model and General Relativity often include features that violate the Weak Equivalence Principle (WEP) and Inverse-Square Law (ISL). A violation of either the WEP or ISL at any length scale would bring into question our fundamental understanding of gravity. Motivated by these considerations, undergraduates and faculty at Humboldt State University are building, and consistently improving upon, an experiment to probe gravitational interactions below the 50-micron length scale. Under high vacuum, we measure the twist of a torsion pendulum as an attractor mass is oscillated nearby in a parallel-plate configuration, providing a time varying torque on the pendulum. The torque variation provides a means to quantify potential deviation from the WEP or ISL at untested distance scales. Recent improvements in analysis and pendulum control will allow the collection of data with unprecedented sensitivity in the near future. | |
Saturday, April 13, 2019 4:42PM - 4:54PM |
D16.00007: Black Hole-Pulsar Binary Tests of Gravity Brian C. Seymour, Kent Yagi Binary pulsars allow precision tests of gravity and have placed stringent bounds on a broad class of theories beyond general relativity. Radio telescopes such as FAST and SKA may discover a pulsar orbiting a black hole in the future. In this talk, we examine the prospects of testing alternative theories of gravity with these black hole-pulsar binaries. In particular, we focus on tests using the orbital decay rate post-Keplerian parameter. We examine gravity with a varying gravitational constant and massive Brans-Dicke theory. Constraints are placed through the simulated measurement accuracy of the orbital decay rate for black hole-pulsar binaries with FAST/SKA. We find that one can constrain the amount of time variation in Newton’s constant G to be slightly weaker than the current strongest bound from solar system experiments, though the former bounds are complementary to the latter since they probe different regime of gravity. Furthermore, we find that a black hole-pulsar binary more strongly constrains the massive Brans-Dicke parameter space, particularly in the low mass sector. These results show that a black hole-pulsar binary allow for more precise tests of gravity. | |
Saturday, April 13, 2019 4:54PM - 5:06PM |
D16.00008: Constraints on parameterized post-Einstenian framework from binary pulsar observations Remya Nair, Nicolás Yunes The parameterized post-Einsteinian (ppE) formalism was proposed to search for generic deviations from general relativity. In this talk we present constraints on the ppE framework obtained from binary pulsar observations. We use measurements of the orbital period decay and post-Keplerian parameters to put bounds on the magnitude of the ppE parameters. Gravitational wave data from coalescing binaries can also be used to do a systematic Bayesian study of the ppE framework and the bounds that we have obtained can be used as an informative prior for such an analysis. | |
Saturday, April 13, 2019 5:06PM - 5:18PM |
D16.00009: Combined Test of Lorentz Symmetry in Short-Range Gravity Cheng-Gang Shao, Ya-Fen Chen, Yu-Jie Tan, Shan-Qing Yang, Jun Luo, Michael Edmund Tobar, Joshua C Long, V Alan Kostelecky, Evan Weisman Tests of the Newtonian inverse square law at short range provide sensitive probes of Lorentz symmetry, violations of which can result in forces varying as the inverse sixth power of distance. We describe a recent search for Lorentz symmetry violation using the short-range experiments at the Huazhong University of Science and Technology (HUST) and Indiana University (IU) [1]. The HUST experiment consists of a torsion pendulum with a rotary source mass and dual compensation to reduce the Newtonian force. The IU experiment uses planar, 1 kHz mechanical oscillators with a stiff conducting shield in between them to suppress backgrounds. After over 2000 total hours of data collected with the former experiment and 40 hours with the latter, no evidence of signals above backgrounds are observed. These results imply constraints on the coefficients of Lorentz violation in the Standard Model Extension at the level of 10^{-12} m^{4}. [1] C.-G. Shao, et al., Phys. Rev. Lett. 122 011102 (2019). |
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