Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session T10: Experimental Test of Gravitation and Gravitational Wave Detectors |
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Sponsoring Units: GGR Chair: Jens Gundlach, University of Washington Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), St. Louis A |
Monday, April 14, 2008 3:30PM - 3:42PM |
T10.00001: Probing Lorentz Symmetry with Equivalence Principle Experiments Jay D. Tasson, V. Alan Kostelecky A potential signal for new physics at the Planck scale is provided by Lorentz-symmetry violation. At presently accessible energies, these violations are described by the Standard-Model Extension (SME). An outline of matter sector of the SME in the presence of gravity will be provided, and new sensitivities to Lorentz violation attainable in Equivalence Principle experiments will be presented. [Preview Abstract] |
Monday, April 14, 2008 3:42PM - 3:54PM |
T10.00002: SME Gravitational Tests Quentin G. Bailey, Alan Kostelecky The search for miniscule Lorentz-symmetry violations offers a promising experimental path to Planck-scale physics. A systematic effective field theory called the Standard-Model Extension (SME) describes general Lorentz violation and has been adopted for modern Lorentz-symmetry tests. In a recent work, the gravitational sector of the SME has been analyzed and sensitive experiments have been identified. In this talk, I will summarize theoretical and experimental aspects of this work. Recent lunar laser ranging and atom interferometer experiments, which place the first stringent constraints on gravity coefficients for Lorentz violation, will be discussed. [Preview Abstract] |
Monday, April 14, 2008 3:54PM - 4:06PM |
T10.00003: Constraints on Lorentz Violation with Precision Measurements of the Lunar Orbit James Battat, John Chandler, Christopher Stubbs Efforts to unify the fundamental forces of nature have produced theories that violate Lorentz symmetry. The Standard Model Extension (SME) has emerged as a comprehensive theoretical framework which parametrizes Lorentz violations. The SME was recently extended to include gravitational interactions, and it was shown that existing Lunar Laser Ranging (LLR) data is sensitive to violations of Lorentz symmetry. LLR measures the Earth-Moon separation by timing the round trip travel of pulsed laser light from a telescope on the Earth to corner cube retroreflectors on the lunar surface. LLR has provided precision measurements of the Earth-Moon separation for nearly 40 years. We present a new analysis of 35 years of archival, LLR data. Our work places the first constraints on six independent linear combinations of SME parameters and we find no evidence for Lorentz symmetry violation at the part in $10^{-6}$ to $10^{-11}$ level in these parameters. Forthcoming millimeter-precision LLR data from the Apache Point Observatory Lunar Laser-ranging Operation (see talk on APOLLO by Thomas Murphy) will further improve these constraints. [Preview Abstract] |
Monday, April 14, 2008 4:06PM - 4:18PM |
T10.00004: Search for Lorentz Violation in a High-Frequency Gravitational Experiment Below 50 microns Josh Long, William Jensen, Sean Lewis We describe an ongoing experimental test of the inverse square law below 50 microns. The experiment uses 1 kHz planar oscillators as test masses with a metal membrane stretched between them to suppress backgrounds, a technique showing promise for probing exceptionally small distances and operation at the limit of instrumental thermal noise. Previous data from this experiment, which set new constraints on short-range phenomena motivated by string models, are being re-analyzed for possible signals of Lorentz violation in the Standard Model Extension. [Preview Abstract] |
Monday, April 14, 2008 4:18PM - 4:30PM |
T10.00005: Test of the Equivalence Principle using Multiple Materials Todd Wagner, Jens Gundlach, Stephan Schlamminger We present new results for a lab test of the equivalence principle. Our experiment uses a torsion pendulum with different composition test bodies arranged in a composition dipole and is mounted on a turntable that rotates with constant angular velocity. We present a combined analysis for Be-Ti and Be-Al composition dipoles, allowing us to constrain equivalence principle violations for charges based upon a linear combination of baryon number and lepton number. Additionally, we present preliminary results for test bodies that mimic the earth's and moon's compositions. [Preview Abstract] |
Monday, April 14, 2008 4:30PM - 4:42PM |
T10.00006: Feasibility of measuring the Shapiro time delay over meter-scale distances Peter Shawhan, Stefan Ballmer, Szabolcs M\'arka The time delay of light as it passes by a massive object, first calculated by Shapiro in 1964, is a hallmark of the curvature of space-time. To date, all measurements of the Shapiro time delay have been made over solar-system distance scales using radio ranging. We show that the new generation of kilometer-scale laser interferometers being constructed as gravitational wave detectors, in particular Advanced LIGO, will be sensitive enough to measure the Shapiro time delay produced by a suitably designed rotating object placed near the laser beam. We show that such an apparatus is feasible (though not easy) to construct, present an example design, and calculate the signal that would be detectable by Advanced LIGO. This offers the first opportunity to measure space-time curvature effects on a laboratory distance scale. [Preview Abstract] |
Monday, April 14, 2008 4:42PM - 4:54PM |
T10.00007: A Conceptual Design for a 4-Satellite Mission to Monitor Variations in The Earth's Gravitational Field Peter L. Bender The GRACE mission has been monitoring time variations in the Earth's gravitational field with much improved accuracy for the past 5 years. A similar follow-on mission to GRACE may fly soon after GRACE. However, it is of interest to explore what could be done in the future if as many as 4 satellites could be employed and they could be flown in a drag-free mode. Laser interferometry would be used between two pairs of satellites with separations of 50 to 100 km. One pair would be in a polar orbit, and the other in a considerably lower inclination orbit. High laser stability would permit high accuracy measurements of short wavelength gravity variations along orbit. A specific mission design that has been suggested to permit more detailed studies is as follows: 312 km altitude for both pairs; a polar orbit for pair-A, with a 79 rev repeat ground track; and a 62.7 deg. inclination for pair-B, with a 360 rev repeat ground track. Pair-B would have a 22.7 day repeat period, 110 km maximum track spacing at temperate latitudes, and many track crossings even near the equator. Pair-A would have a 5 day repeat period, which would help in monitoring fairly rapid variations in the Earth's field. [Preview Abstract] |
Monday, April 14, 2008 4:54PM - 5:06PM |
T10.00008: New Laser Technologies for Gravitational Wave Detectors Mihai Bondarescu, Ruxandra Bondarescu, Yanbei Chen, Oleg Kogan, Andrew Lundgren, David Tsang Thermal noise is expected to be the dominant source of noise in the most sensitive frequency band of second generation ground based gravitational wave detectors. Reducing it as much as possible is of paramount importance for increasing detector sensitivity and observing not only gravitational waves, but also quantum phenomena such as entanglement of 40 kg objects. Reshaping the beam to a flatter wider profile which probes more of the mirror surface reduces this noise. The ``Mesa'' beam shape has been proposed for this purpose and for a long time it has been regarded as the leading low-noise beam for LIGO. We have shown that thermal noise can be reduced by 12\% with no additional effort by using finite mirror effects to our advantage rather then working against them. A reduction of 28\% can be obtained by reshaping the mirror to coincide with the phase front of the real beam instead of a theoretical beam modeled with infinite mirroers. A drastic reduction in thermal noise by as much as 60\% can be obtained by moving away from Mesa altogether and using a beam supported by conical mirrors that resemble the Bessel-Gauss beams. If the maximum 60\% reduction in thermal noise is achieved, then in the most sensitive frequency band, LIGO will see up to three times more events. [Preview Abstract] |
Monday, April 14, 2008 5:06PM - 5:18PM |
T10.00009: Gravitational probes of string theory and quantum gravity Nicolas Yunes The Chern-Simons modification to General Relativity is an effective theory that represents both a low-energy limit of all string theories as well as loop quantum gravity. The main modification is the introduction of a parity-violating, Pontryagin term to the Einstein-Hilbert action, which has already been successfully employed to resolve the leptogenesis problem and anisotropies in the CMB. In this talk, I shall discuss gravitational probes of this modification, focusing on solar system experiments and gravitational wave tests. A parameterized post-Newtonian analysis will show that Chern-Simons gravity leads to a correction to gyroscopic precession that could be detected with Gravity Probe B or LAGEOS. A gravitational wave analysis leads to an ``amplitude birefringence'' effect that could be detected with gravitational wave interferometers, possibly leading to stronger tests of the modified theory. The proposed tests constitute gravitational probes of the quantum structure of spacetime on local and cosmological scales. [Preview Abstract] |
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