Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session B3: Tests of General Relativity and Alternatives: Theory Meets ExperimentUndergraduate
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Sponsoring Units: DGRAV Chair: Clifford Will, University of Florida - Gainesville Room: Maryland C |
Saturday, January 28, 2017 10:45AM - 10:57AM |
B3.00001: Testing gravity with Lunar Laser Ranging: An update on the APOLLO experiment James Battat, Nick Colmenares, Rodney Davis, Louisa Huang Ruixue, Thomas W. Murphy, Jr. The mystery of dark energy and the incompatibility of quantum mechanics and General Relativity indicate the need for precision experimental probes of gravitational physics. The Earth-Moon-Sun system is a fertile laboratory for such tests. The Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) makes optical range measurements to retro-reflectors on the Moon with one millimeter precision. These measurements of the lunar orbit enable incisive constraints on gravitational phenomena such as the Strong Equivalence Principle and $dG/dt$ (among others). Until now, the APOLLO team had not been able to assess the accuracy of our data, in large part because known limitations to lunar range models ensure data-model residuals at the centimeter scale. To directly measure the APOLLO system timing accuracy, we have built an Absolute timing Calibration System (ACS) that delivers photons to our detector at known, stable time intervals using a pulsed fiber laser locked to a cesium frequency standard. This scheme provides real-time calibration of the APOLLO system timing, synchronous with the range measurements. We installed the calibration system in August, 2016. In this talk, we will describe the ACS design, and present present preliminary results from the ACS calibration campaign. [Preview Abstract] |
Saturday, January 28, 2017 10:57AM - 11:09AM |
B3.00002: Alternative theories of gravity and Lorentz violation Rui Xu, Joshua Foster, V. Alan Kostelecky General relativity has achieved many successes, including the prediction of experimental results. However, its incompatibility with quantum theory remains an obstacle. By extending the foundational properties of general relativity, alternative theories of gravity can be constructed. In this talk, we focus on fermion couplings in the weak-gravity limit of certain alternative theories of gravity. Under suitable experimental circumstances, some of these couplings match terms appearing in the gravitational SME, which is a general framework describing violations of local Lorentz invariance. Existing limits on Lorentz violation can therefore be used to constrain certain Lorentz-invariant alternative theories of gravity. [Preview Abstract] |
Saturday, January 28, 2017 11:09AM - 11:21AM |
B3.00003: Testing gravity at the micron scale using optically trapped nanospheres Andrew Geraci, Gambhir Ranjit, Mark Cunningham, Kirsten Casey According to several theories beyond the Standard Model, Yukawa-type corrections to Newtonian gravity may occur at micrometer length scales. I will discuss our experiment dedicated to searching for these forces using laser-cooled silica nanospheres in an optical standing-wave trap. Using this system we have demonstrated calibrated force sensing at the zeptonewton level. The nanospheres can act as a sensor for short-range Yukawa-forces when levitated near a microfabricated source mass. [Preview Abstract] |
Saturday, January 28, 2017 11:21AM - 11:33AM |
B3.00004: Spin Precessing Black Hole Binaries in Dynamical Chern-Simons Gravity Nicholas Loutrel, Nicolas Yunes, Takahiro Tanaka Spinning black holes in binary systems under go spin precession, as well as precession of the orbital plane, as a result of the coupling between the black hole spins and the orbital angular momentum. This effect introduces an observable modulation in the amplitude of the gravitational waves emitted by the binary. In dynamical Chern-Simons gravity, spinning black holes are modified from General Relativity through the presence of a scalar dipole moment, which is proportional to the spin of the black hole. Such additional degrees of freedom modify the spin precession equations, and thus the observable modulation of the gravitational waves. In this talk, I will discuss how to approach the spin precession of black holes in dynamical Chern-Simons gravity from an effective field theory perspective and discuss how the modulation of gravitational waves differs from General Relativity. [Preview Abstract] |
Saturday, January 28, 2017 11:33AM - 11:45AM |
B3.00005: Hamiltonian formalism for Perturbed Black Hole Spacetimes Deyan Mihaylov, Jonathan Gair Present and future gravitational wave observations provide a new mechanism to probe the predictions of general relativity. Observations of extreme mass ratio inspirals with millihertz gravitational wave detectors such as LISA will provide exquisite constraints on the spacetime structure outside astrophysical black holes, enabling tests of the no-hair property that all general relativistic black holes are described by the Kerr metric. Previous work to understand what constraints LISA observations will be able to place has focussed on specific alternative theories of gravity, or generic deviations that preserve geodesic separability. We describe an alternative approach to this problem — a technique that employs canonical perturbations of the Hamiltonian function describing motion in the Kerr metric. We derive this new approach and demonstrate its application to the cases of a slowly rotating Kerr black hole which is viewed as a perturbation of a Schwarzschild black hole, of coupled perturbations of black holes in the second-order Chern-Simons modified gravity theory, and several more indicative scenarios. [Preview Abstract] |
Saturday, January 28, 2017 11:45AM - 11:57AM |
B3.00006: Relativistic stars in scalar-tensor theories with disformal coupling Hector O. Silva, Masato Minamitsuji We discuss a general formulation to study the structure of slowly-rotating relativistic stars in a broad class of scalar-tensor theories including disformal coupling to matter. Our approach includes as particular cases theories with generalized kinetic terms and generic scalar field potentials, and contains theories with conformal coupling as particular limits. We propose a minimal model to investigate the role of the disformal coupling on the non-perturbative effect known as spontaneous scalarization, which causes relativistic star solutions in certain classes of scalar-tensor theories to differ dramatically from their general relativistic counterparts. Moreover, we show that the moment of inertia and compactness of stars are equation of state independent, which can potentially be used to constrain the model observationally. [Preview Abstract] |
Saturday, January 28, 2017 11:57AM - 12:09PM |
B3.00007: Biconformal Compactification Benjamin Lovelady, James Wheeler The gauging of the conformal group of n-dim Euclidean space by the homogenous Weyl group leads to a principal bundle known as biconformal space. Time arises naturally on a 2n-dimensional symplectic manifold with SO(n) spanning the fibers. These spaces allow a scale-invariant first-order gravity action, making them ideal candidates for quantizable gravity. We investigate the effect of including m compact dimensions beyond the 4 of spacetime. This gives 2m extra dimensions on the symplectic manifold that need to be compactified. Various compactifications lead to different fields, but for m=1,2 the set of compactifications is countable. [Preview Abstract] |
Saturday, January 28, 2017 12:09PM - 12:21PM |
B3.00008: The Spacetime Between Einstein and Kaluza-Klein: Further Explorations Chris Vuille Tensor multinomials can be used to create a generalization of Einstein's general relativity that in a mathematical sense falls between Einstein's original theory in four dimensions and the Kaluza-Klein theory in five dimensions. In the extended theory there are only four physical dimensions, but the tensor multinomials are expanded operators that can accommodate other forces of nature. The equivalent Ricci tensor of this geometry yields vacuum general relativity and electromagnetism, as well as a Klein-Gordon-like quantum scalar field. With a generalization of the stress-energy tensor, an exact solution for a plane-symmetric dust can be found where the scalar portion of the field drives early universe inflation, levels off for a period, then causes a later continued universal acceleration, a possible geometric mechanism for the inflaton or dark energy. Some new explorations of the equations, the problems, and possibilities will be presented and discussed. [Preview Abstract] |
Saturday, January 28, 2017 12:21PM - 12:33PM |
B3.00009: Constraining Gravity at Large Scales with Clusters of Galaxies D. Rapetti, M. Cataneo, F. Schmidt, L. Lombriser, B. Li, A. Mantz, S. Allen, D. Applegate, P. Kelly, A. von der Linden, R. G. Morris I will present the most recent constraints on $f(R)$ modifications of gravity from the abundance of massive galaxy clusters. Our analysis self-consistently and simultaneously incorporates survey, observable-mass scaling relations, as well as weak gravitational lensing data to accurately calibrate the absolute cluster mass scale. Using this advanced cluster analysis in combination with CMB data, and other cosmological constraints, we obtain upper bounds on $f(R)$ gravity that are about an order of magnitude tighter than those from such previous studies. The robustness of our results derives from our high quality cluster growth data out to redshifts $z\sim0.5$, a tight control of systematic uncertainties, accounting for the covariance between all parameters, and the use of the full shape of the halo mass function (HMF) over the mass range of the data. Based on the current highest resolution N-body simulations, I will also describe our new modeling of the $f(R)$ HMF. This includes novel corrections to capture key non-linear effects of the Chameleon screening mechanism that will allow us to obtain the next generation of cluster constraints on this model. [Preview Abstract] |
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