Test of the gravitational redshift with stable clocks in eccentric orbits: application to Galileo satellites 5 and 6

TL;DR

This paper proposes using Galileo satellites in eccentric orbits to perform a more precise test of the gravitational redshift, a key aspect of Einstein's Equivalence Principle, potentially improving previous experimental limits.

Contribution

It introduces a novel method utilizing stable clocks on eccentric orbit satellites to enhance the precision of gravitational redshift tests beyond past experiments.

Findings

Potential to improve the gravitational redshift test uncertainty to (3-4)×10⁻⁵

Use of realistic noise and systematic effects in the analysis

Application to Galileo satellites 5 and 6 for extended data collection

Abstract

The Einstein Equivalence Principle (EEP) is one of the foundations of the theory of General Relativity and several alternative theories of gravitation predict violations of the EEP. Experimental constraints on this fundamental principle of nature are therefore of paramount importance. The EEP can be split in three sub-principles: the Universality of Free Fall (UFF), the Local Lorentz Invariance (LLI) and the Local Position Invariance (LPI). In this paper we propose to use stable clocks in eccentric orbits to perform a test of the gravitational redshift, a consequence of the LPI. The best test to date was performed with the Gravity Probe A (GP-A) experiment in 1976 with an uncertainty of $1.4\times10^{-4}$. Our proposal considers the opportunity of using Galileo satellites 5 and 6 to improve on the GP-A test uncertainty. We show that considering realistic noise and systematic effects, and thanks to a highly eccentric orbit, it is possible to improve on the GP-A limit to an uncertainty around $(3-4)\times 10^{-5}$ after one year of integration of Galileo 5 and 6 data.