Impact of correlated seismic and correlated Newtonian noise on the Einstein Telescope

Abstract

Correlated noise could impact the search for the gravitational wave background at future Earthbased gravitational-wave detectors. Due to the small distance (∼ 400 m) between the different interferometers of the Einstein Telescope, correlated seismic noise could have a significant effect. To this extent, we study the seismic correlations at the Earth's surface, as well as underground, between seismometers and geophones separated by several hundreds of meters, in the frequency range 0.05 Hz -50 Hz. Based on these correlated seismic fields we predict the levels of correlated Newtonian noise (NN). We construct upper limits on the allowed seismic coupling function such that correlated seismic noise does not affect the search for an isotropic gravitational wave background. Assuming a facility located 300 m below the surface, the impact on the search for a gravitational wave background of correlated NN from Rayleigh waves are found to be problematic up to ∼ 5 Hz. The NN from body waves, however, constitutes a serious threat to the search of a gravitational wave background. Correlated NN from body waves could be up to five to seven orders of magnitude above the planned sensitivity at ∼ 3 Hz and it could impede any search for a gravitational wave background below 40 Hz. With a factor 10 of NN reduction via NN cancellation in each interferometer, the effects of the NN on the stochastic search could be eliminated above 30 Hz.

Joint optimization of seismometer arrays for the cancellation of Newtonian noise from seismic body waves in the Einstein Telescope

“…The triangular shape of ET entails that the input TMs of an interferometer will be close to the end TMs of two other interferometers. Correlations of NN between TMs and seismic correlations were taken into account in our study (see also [10] for a study on the impact of correlated noise in ET). The optimal arrays calculated in this study minimized the residuals simultaneously in three interferometers.…”

“…In the NN literature, the value p = 1/3 was typically used [1,2,8,10]. This assumption was made because the composition of the seismic was not known for sites of interest, and so the ad hoc assumption was made that the energy is equipartitioned among the three polarizations (one compressional mode and two shear modes).…”

Prospects for LISA to detect a gravitational-wave background from first order phase transitions

“…Here, the focus is on whether we can separate the PT GW background from the instrument noise and astrophysical foregrounds. We note too that a recent study of the triangular configuration for non-equal detector noise and non-equal noise correlations changes the properties of the A and E channels [59]. Using the channels A and E without channel T would increase the uncertainties of the parameter estimation, especially for values near the level of detectability (Ω p ∼ 3 × 10 −11 , presented below).…”

Stochastic gravitational wave background: Methods and implications

“…Due to their co-located nature correlated noise could be expected. There have been several studies investigating correlated magnetic noise at the ET [158,138] as well as correlated seismic and Newtonian noise [191]. Based on LISA pathfinder data also some preliminary noise correlation studies have been performed [192].…”