Bounds on gravitational wave backgrounds from large distance clock comparisons

TL;DR

This paper introduces a novel method for constraining gravitational wave backgrounds by comparing ultra-stable clocks between ground stations and spacecraft, potentially improving current bounds in specific frequency ranges.

Contribution

It proposes a new clock comparison technique for setting bounds on gravitational wave backgrounds, enhancing sensitivity over existing methods.

Findings

The method can significantly improve bounds on gravitational wave backgrounds.

Optimization of the technique depends on signal and noise characteristics.

Application to SAGAS project demonstrates practical feasibility.

Abstract

Our spacetime is filled with gravitational wave backgrounds that constitute a fluctuating environment created by astrophysical and cosmological sources. Bounds on these backgrounds are obtained from cosmological and astrophysical data but also by analysis of ranging and Doppler signals from distant spacecraft. We propose here a new way to set bounds on those backgrounds by performing clock comparisons between a ground clock and a remote spacecraft equipped with an ultra-stable clock, rather than only ranging to an onboard transponder. This technique can then be optimized as a function of the signal to be measured and the dominant noise sources, leading to significant improvements on present bounds in a promising frequency range where different theoretical models are competing. We illustrate our approach using the SAGAS project which aims to fly an ultra stable optical clock in the outer solar system.