Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session Q11: Experimental Tests of Gravitation |
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Sponsoring Units: GGR GPMFC Chair: Eric Adelberger, University of Washington Room: Plaza Court 1 |
Monday, May 4, 2009 10:45AM - 10:57AM |
Q11.00001: Next Generation of Lunar Laser Ranging Instruments Stephen Merkowitz, David Arnold, Philip Dabney, Jeffrey Livas, Jan McGarry, Gregory Neumann, Thomas Zagwodzki Laser ranging over the past 40 years to retroreflector arrays placed on the lunar surface by the Apollo astronauts and the Soviet Luna missions have dramatically increased our understanding of gravitational physics along with Earth and Moon geophysics, geodesy, and dynamics. The precision of the range measurements has historically been limited by the ground station capabilities. With the APOLLO instrument at the Apache Point facility in New Mexico now routinely achieving sub-centimeter level precision, future measurements are likely to be limited by errors associated with the Apollo retroreflectors. In addition, the clustering of the lunar arrays and similar latitudes of the available lunar ranging stations weakens our ability to precisely measure the lunar librations. Advanced retroreflectors placed at locations far from the Apollo sites would enable the study of additional effects, particularly those that rely on the measurement of the lunar librations. Active laser transponders are also under development that can provide a strong enough signal to enable the use of most of the more than 40 existing satellite laser ranging stations to make frequent range measurements, even during the daytime. We report here on a recent study of possible next generation lunar laser ranging instruments that will be ready for NASA's return to the Moon. [Preview Abstract] |
Monday, May 4, 2009 10:57AM - 11:09AM |
Q11.00002: A WEP Test on a Sounding Rocket Robert Reasenberg, Bijunath Patla, James Phillips, Eugeniu Popsecu We are developing a payload for detecting a possible violation of the weak equivalence principle (WEP) while on a sounding rocket's free-fall trajectory. We estimate an uncertainty of $10^{-16}$ from a single flight. The experiment consists of 8 drops, each lasting 40 s, of the two test mass assemblies (TMA). The instrument orientation will be reversed between successive drops, which reverses the signal but leaves most systematic errors unchanged. Each TMA consists of a pair of cubes connected by a short rod. The four cubes are in a square lying in a plane perpendicular to the symmetry axis (z axis) of the payload and close to its CM. At a distance of 0.3 m along the z axis, there is a highly stable plate that holds four of our tracking frequency laser gauges, which measure the distances to the cubes. The TMA are surrounded by capacitance plates, which allow both measurement and control of position and orientation. During the brief night-time flight, the payload outside temperature drops slowly from around 300 K. Temperature stability of the instrument is essential and we can achieved it passively. This work was Supported in part by NASA grant NNX08AO04G. [Preview Abstract] |
Monday, May 4, 2009 11:09AM - 11:21AM |
Q11.00003: Testing Theories of Gravity Using Galactic Center Stars David Merritt, Seppo Mikkola, Clifford Will, Tal Alexander, Stefan Harfst Stars orbiting very close to the supermassive black hole at the center of the Milky Way will experience precession of their orbital planes induced by relativistic frame dragging and by the quadrupolar gravity of the hole, at levels that are potentially observable using adaptive optics on the next generation of large ground-based telescopes. Astrometric observations of the orbits of at least two such stars can in principle lead to a determination of the angular momentum vector of the black hole and its quadrupole moment, allowing a test of the general relativistic no-hair theorems. We present the first relativistic N-body simulations of stellar motions around the Milky Way black hole and evaluate the degree to which orbital precession would be influenced by Newtonian perturbations from other stars and from compact stellar remnants. [Preview Abstract] |
Monday, May 4, 2009 11:21AM - 11:33AM |
Q11.00004: Constraining Modified Gravity with SN 1987A Phillip Zukin, Edmund Bertschinger In the 1950's, Papapetrou found that extended bodies with spin, in general relativity, do not move along geodesics because of a spin-curvature coupling. Using an Eikonal approximation, we reproduce these results for Dirac and Majorana particles. We generalize these results to modified theories of gravity with a non-minimally coupled matter lagrangian and place constraints on the coupling field based on the arrival times of SN 1987A neutrinos. [Preview Abstract] |
Monday, May 4, 2009 11:33AM - 11:45AM |
Q11.00005: Modification to the Luminosity Distance Redshift Relation in Modified Gravity Theories Eran Rosenthal, Eanna Flanagan, Ira Wasserman We derive an expression for the luminosity distance as a function of redshift for a flat Robertson-Walker spacetime perturbed by arbitrary scalar perturbations possibly produced by a modified gravity theory with two different scalar perturbation potentials. Measurements of the luminosity distance as function of redshift provide a constraint on a combination of the scalar potentials and so they can complement weak lensing and other measurements in trying to distinguish among the various alternative theories of gravity. [Preview Abstract] |
Monday, May 4, 2009 11:45AM - 11:57AM |
Q11.00006: Relativistic Orbits in a Keplerian Limit Antonio Mondragon An approximate closed-form solution to the relativistic central-mass problem in a Keplerian limit is presented. This solution is limited to describing approximately elliptical (Keplerian) orbits, and provides orbital characteristics as relativistic corrections to the Keplerian orbits of classical mechanics. It is emphasized that (Schwarzschild) geometry alone predicts deviations from classical orbits, including precession, reduced radial coordinate, and increased eccentricity. The predicted rate of precession is in agreement with the established result, correctly describing precession of perihelia of the inner planets. Relativistic corrections to the radial coordinate and eccentricity are of the same order of magnitude as the rate of precession and may provide further verifications of general relativity. The results may also be applied to isolated binary systems. [Preview Abstract] |
Monday, May 4, 2009 11:57AM - 12:09PM |
Q11.00007: ABSTRACT WITHDRAWN |
Monday, May 4, 2009 12:09PM - 12:21PM |
Q11.00008: Bounds upon Graviton mass, and making use of the difference between Graviton propagation speed and HFGW transit speed to observe post Newtonian corrections to Gravitational potential fields Andrew Beckwith The author presents a post Newtonian approximation based upon an earlier argument / paper by Clifford Will as to Yukawa revisions of gravitational potentials in part initiated by gravitons with explicit mass dependence in their Compton wave length. The Li- Baker detector, with its ultra refined capacity to obtain relic HFGW signals is able to experimentally determine for HFGW empirical data sets which could determine upper bounds as to the existence of a graviton mass. Prior work with Clifford Will's idea was stymied by the application to binary stars and other such astro-physical objects with non useful frequencies topping off as up to 100 Hertz, thereby rendering Yukawa modifications of Gravity due to gravitons effectively an experimental curiosity which was not testable with any known physics equipment. The appearance of HFGW data sets as could be measured by the Li Baker detector gives a real chance as to experimentally obtain a measurable upper bound to the Compton wave length of Gravitons, which leads to other tests as to Gravitons existence as a measurable quantity, contradicting Tony Rothman's (2006) assertion that a detector the size of Jupiter would be needed to obtain measurements of a single graviton. [Preview Abstract] |
Monday, May 4, 2009 12:21PM - 12:33PM |
Q11.00009: Search for Large Extra Dimensions via Observations of Neutron Stars with Fermi--LAT Bijan Berenji, Elliott Bloom Large extra dimensions (LED) have been proposed to account for the apparent weakness of gravitation. These theories also indicate that the postulated massive Kaluza-Klein (KK) gravitons may be produced by nucleon-nucleon bremsstrahlung in the course of core collapse of supernovae. Hannestad and Raffelt have predicted energy spectra of gamma ray emission from the decay of KK gravitons trapped by the gravity of the remnant neutron stars (NS). These and other authors have used EGRET data on NS to obtain stringent limits on LED. Fermi-LAT is observing radio pulsar positions obtained from radio and x-ray catalogs. NS with certain characteristics are unlikely emitter of gamma rays, and emit in radio and perhaps x-rays. This talk will focus on the blind analysis we plan to perform, which has been developed using the 1$^{st}$ 2 months of all sky data and Monte Carlo simulations, to obtain limits on LED based on about 1 year of Fermi-LAT data. Preliminary limits from this analysis using these first 2 months of data will be also be discussed. [Preview Abstract] |
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