Characterizing Earth gravity field fluctuations with the MIGA antenna for future gravitational wave detectors

Fluctuations of the Earth's gravitational field are a major noise source for ground-based experiments investigating general-relativistic phenomena such as gravitational waves (GWs). Mass density variations caused by local seismic or atmospheric perturbations determine spurious differential displacements of the free-falling test masses-called gravity gradient noise (GGN)-which mimics GW effects. This GGN is expected to become dominant in the infrasound domain and must be tackled for the future realization of observatories exploring GWs at low frequency. GGN will be studied with the MIGA experiment, a demonstrator for low-frequency GW detection based on atom interferometry currently being constructed at the low-noise underground Laboratoire Souterrain à Bas Bruit (LSBB) in France. MIGA will provide precise measurements of local gravity, probed by a network of three free-falling atom test masses separated by up to 150 m. We model the effect of GGN for MIGA and use seismic and atmospheric data recorded at LSBB to characterize their impact on future measurements. We show that the antenna will be able to characterize GGN using dedicated data analysis methods.