Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session A11: Lorentz Symmetry in Gravitation; followed by LISA Developments |
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Sponsoring Units: GGR GPMFC Chair: Michael Seifert, Indiana University, and Guido Mueller, University of Florida Room: Maryland C |
Saturday, February 13, 2010 8:30AM - 8:42AM |
A11.00001: New Tests of Lorentz Violation in Electromagnetism Matthew Mewes, Alan Kostelecky Tests of Lorentz invariance involving photons have provided some of the best constraints on possible violations of this fundamental symmetry. To date, most studies have focused primarily on Lorentz-violating operators of renormalizable dimension. However, other operators exist and may lead to interesting effects in photons. In this talk, we consider Lorentz-violating operators of arbitrary dimension within electromagnetism. Several features emerge that are not present in the renormalizable case. We discuss the experimental consequences, including those in astrophysical searches for dispersion and birefringence and laboratory-based experiments. A classification based on the physical effects is given. [Preview Abstract] |
Saturday, February 13, 2010 8:42AM - 8:54AM |
A11.00002: Spontaneous Lorentz symmetry breaking and topological defects Michael Seifert ``Lorentz-violating'' theories, in which Lorentz symmetry is spontaneously broken via a vacuum expectation value of a vector or tensor field, have been the subject of much interest in recent years. It is well-known (from other contexts) that spontaneously broken symmetries can give rise to topological defects. I will discuss the possible topological defects that can arise in Lorentz-violating theories. The types of topological defects occurring in a given theory depends critically on the rank and symmetry structure of the Lorentz-violating tensor field involved; for appropriate choices of tensor field, domain wall solutions and monopole solutions can be found. The stability and the cosmological implications of these field configurations will also be discussed. [Preview Abstract] |
Saturday, February 13, 2010 8:54AM - 9:06AM |
A11.00003: Current and future tests of Lorentz symmetry in gravitational systems Quentin Bailey Recently, there have been a growing number of experiments searching for tiny violations of Lorentz symmetry. These tests are motivated by the possibility of uncovering experimental signals from an underlying unified theory of physics at the Planck scale. The Standard-Model Extension (SME) is a theoretical framework describing general Lorentz violation for known matter and fields, including gravity. In this talk, I will discuss the theoretical and experimental work on gravitational experiments testing Lorentz symmetry, including recent solar system and Earth-based laboratory tests, as well as possible future tests. [Preview Abstract] |
Saturday, February 13, 2010 9:06AM - 9:18AM |
A11.00004: Einstein-Aether Inflation William Donnelly, Ted Jacobson Einstein-aether theory is a Lorentz-violating theory of gravity with a timelike vector field that plays the role of a preferred frame or ``aether''. Although Lorentz-violating couplings to standard model particles are tightly constrained observationally, much less is known about Lorentz-violating couplings of the inflaton. The aether allows us to consider terms in the action that depend explicitly on the rate of expansion, which would not be possible in a Lorentz-invariant theory. We therefore consider the unique aether-inflaton coupling of mass dimension two: the time derivative of the inflaton in the aether frame. The effect of this term is proportional to the Hubble factor, making it irrelevant today but important during inflation. We first show that the theory is viable by deriving conditions for stability of linearized perturbations about flat spacetime, and conclude by showing how the new coupling changes the homogeneous dynamics of the cosmology during inflation. [Preview Abstract] |
Saturday, February 13, 2010 9:18AM - 9:30AM |
A11.00005: Solutions to a Modified Newtonian Dynamics Force Law Ronald Mickens We consider a specific relation for a modified Newtonian force law\footnote{M. Milgrom, Astrophysical J., Vol. 270 (1983), 365.} in one space dimension: \[ \frac{m|a|a}{(a_0+|a|)}=F(x),\] where $a=d^2x/dt^2$ and $a_0$ is a very small ``cosmic'' related acceleration.\footnote{J. H. Gundlach, et al., Phys. Rev. Letters. Vol. 98 (2007), 150801.} Exact solutions are calculated for zero, constant, and linear damping forces. However, the linear harmonic oscillator force situation could not be solved exactly and, as a consequence, an approximation to the periodic solutions was determined. To check the consistency of the calculations, we took the $a_0\to 0$ limits and found that the prior known results were obtained for all four systems. [Preview Abstract] |
Saturday, February 13, 2010 9:30AM - 9:42AM |
A11.00006: Mitigation of Laser Frequency Noise in LISA Interferometry James Ira Thorpe The Laser Interferometer Space Antenna (LISA) is a proposed detector of gravitational waves in the $0.1\,\mbox{mHz}-0.1\,\mbox{Hz}$ band. LISA will measure gravitational wave strain at the $10^{-21}$ level by monitoring the distance between freely-falling test masses separated by baselines of $5\times10^{9}\,\mbox{m}$ with a precision of roughly $10^{-11}\,\mbox{m}$. These distance measurements will be made using heterodyne interferometry with multiple light sources on moving spacecraft with changing baselines, all of which cause frequency noise to couple into the displacement measurement. I will describe how LISA interferometry mitigates the effects of laser frequency noise through active suppression and common mode rejection. Recent laboratory developments will also be discussed. [Preview Abstract] |
Saturday, February 13, 2010 9:42AM - 9:54AM |
A11.00007: Laser Communications for LISA and the University of Florida LISA Interferometry Simulator Dylan Sweeney, Justin Cohen, Simon Barke, Shawn Mitryk, Vinzenz Wand, Guido Mueller The LISA mission uses laser interferometry to measure fluctuations in the path length between the spacecraft caused by gravitational waves. For LISA to be successful the spacecraft must be able to communicate with each other in order to transfer clock signals, measure the range between the spacecraft, and to share recorded data. All of these functions will be accomplished using the laser links between the spacecraft. The University of Florida LISA Interferometry Simulator (UFLIS) is capable of simulating LISA interferometry with realistic delay times between the spacecraft by utilizing an electronic phase delay technique. We plan to upgrade the UFIS to include the laser communication systems, and present the work towards this goal that has already been accomplished. [Preview Abstract] |
Saturday, February 13, 2010 9:54AM - 10:06AM |
A11.00008: Time-Delay Interferometry Simulations and Gravitational Wave Extraction at the University of Florida Interferometric Simulator Shawn Mitryk, Vinzenz Wand, Alix Preston, Guido Mueller, David Tanner The Laser Interferometer Space Antenna (LISA) is a NASA/ESA space mission with the goal of measuring gravitational waves (GW) at frequencies of 30 uHz - 1 Hz. Going to space avoids seimic and gravity-gradient noise which limit all ground-based detectors. LISA will measure the spatial changes between drag-free proof masses separated by a distance of 5 Gm using heterodyne interferometry. The laser noise must be recorded and removed from the measurement through time-delay interferometry (TDI) to extract gravitational wave signals. The University of Florida LISA Interferometry Simulator (UFLIS) performs hardware-in-the-loop simulations of LISA by reproducing the expected pre-stabilized laser noise, delaying the laser frequency noise by the light-travel time along the LISA arms, injecting mock gravitational wave signals, and forming the required TDI combinations to extract the injected GW signals. Using the UFLIS, we present the extraction of mock GW signals buried under 9 orders of magnitude of laser frequency noise. [Preview Abstract] |
Saturday, February 13, 2010 10:06AM - 10:18AM |
A11.00009: Arm locking experiments on UFLIS Yinan Yu, Guido Mueller The Laser Interferometer Space Antenna (LISA) will detect gravitational waves in the frequency region of $3\times10^{-5}\;\rm{Hz}$ to $1\; \rm{Hz}$ by means of laser interferometry. At the University of Florida we developed the University of Florida LISA Interferometer Simulator (UFLIS) in order to study and verify laser frequency noise reduction and suppression techniques under realistic LISA-like conditions. These conditions include the Doppler shifts between the spacecraft, LISA-like signal travel times, and realistic laser frequency and timing noise. One of the proposed laser frequency stabilization techniques in LISA is arm locking, which synthesizes an adequately filtered linear combination of the LISA interferometry signals as a frequency reference. The arm locking experiments on UFLIS have already demonstrated the capability of single arm locking integrated with tunable cavity pre-stabilization as well as in the presence of a Doppler knowledge error. In this presentation we will report about experiments on advanced arm locking schemes such as dual arm locking and modified dual arm locking. We will demonstrate the noise suppression performance of dual arm locking and the capability of modified dual arm locking sensor to alleviate the frequency pulling effect due to the Doppler error. Furthermore, the limits of different noise sources such as digitization noise and clock noise in our experiments will also be discussed. This work is supported by NASA grant 07-ATFP07-0116. [Preview Abstract] |
Saturday, February 13, 2010 10:18AM - 10:30AM |
A11.00010: Testbed for LISA photodetectors Felipe Guzman, Jeffrey Livas, Robert Silverberg The Laser Interferometer Space Antenna (LISA) is a gravitational wave observatory consisting of three spacecraft separated by 5 million km in an equilateral triangle whose center follows the Earth in orbit around the Sun but offset in orbital phase by 20 degrees. LISA is designed to observe sources in the frequency range of 0.1\,mHz--100\,mHz by measuring fluctuations of the inter-spacecraft separation with laser interferometry. Quadrant photodetectors are used to measure both separation and angular orientation. Noise level, phase and amplitude inhomogeneities of the semiconductor response, and channel cross-talk between quadrant cells need to be assessed in order to ensure the $10\,\mathrm{pm}/\sqrt{Hz}$ sensitivity required for the interferometric length measurement in LISA. To this end, we are currently developing a testbed that allows us to evaluate photodetectors to the sensitivity levels required for LISA. A detailed description of the testbed and prelimary results will be presented. [Preview Abstract] |
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