Session D16: Tests of General Relativity I

A New Multi-mode Apparatus to Determine G

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.   

Tests of General Relativity with the Binary Black Hole Signals from the LIGO-Virgo Catalog GWTC-1

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.   

Testing Gravity Below 50 micrometers

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.    

Constraints on parameterized post-Einstenian framework from binary pulsar observations

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.