"Imprinting" in General Relativity Tests?

TL;DR

This paper examines how the assumptions of general relativity might bias spacecraft-based tests of gravity, especially in high-precision measurements of the PPN parameter gamma, and discusses implications for future experiments.

Contribution

It identifies potential biases in solar system tests of gravity caused by the prior assumptions of general relativity, highlighting their impact on future high-precision measurements.

Findings

Imprinting of general relativity can bias measurements of gamma by about 10^-6.

Current experiments like Cassini are unaffected by this bias.

Future experiments aiming for 10^-7 to 10^-9 accuracy could be significantly affected.

Abstract

We investigate possible a-priori "imprinting" of general relativity itself on spaceraft-based tests of it. We deal with some performed or proposed time-delay ranging experiments in the Sun's gravitational field. The "imprint" of general relativity on the Astronomical Unit and the solar gravitational constant GM_\odot, not solved for in the so far performed spacecraft-based time-delay tests, may induce an a-priori bias of the order of 10^-6 in typical solar system ranging experiments aimed to measuring the space curvature PPN parameter \gamma. It is too small by one order of magnitude to be of concern for the performed Cassini experiment, but it would affect future planned or proposed tests aiming to reach a 10^-7-10^-9 accuracy in determining \gamma.