Progress in Lunar Laser Ranging Tests of Relativistic Gravity
Abstract
Analyses of laser ranges to the Moon provide increasingly stringent limits on any violation of the Equivalence Principle (EP); they also enable several very accurate tests of relativistic gravity. We report the results of our recent analysis of Lunar Laser Ranging (LLR) data giving an EP test of (MG/MI)EP =(-1.0 +/- 1.4) x 10-13. This result yields a Strong Equivalence Principle (SEP) test of (MG/MI)SEP =(-2.0 +/- 2.0) x 10-13. Also, the corresponding SEP violation parameter η is (4.4 +/- 4.5) x 10-4, where η=4β-γ-3 and both β and γ are parametrized post-Newtonian (PPN) parameters. Using the recent Cassini result for the parameter γ, PPN parameter β is determined to be β-1=(1.2 +/- 1.1) x 10-4. The geodetic precession test, expressed as a relative deviation from general relativity, is Kgp=-0.0019 +/- 0.0064. The search for a time variation in the gravitational constant results in G/G=(4 +/- 9) x 10-13 yr-1, consequently there is no evidence for local (~1AU) scale expansion of the solar system.
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