A lower limit for Newtonian-noise models of the Einstein Telescope

Abstract The Einstein Telescope (ET) is a proposed third-generation gravitational-wave (GW) underground observatory. It will have greatly increased sensitivity compared to current GW detectors, and it designed extend the observation band down few Hz. At these frequencies, major limitation of ET predicted be due gravitational fluctuations produced by environment, most importantly seismic field, which give rise so-called Newtonian noise (NN). Accurate models NN are crucial assess compatibility an candidate site with target also considering possible reduction in cancellation. With becoming increasingly complex as they include details geology topography, tools make robust assessments their accuracy. For this purpose, we derive lower bound on spectra, weakly dependent properties field. As first application, use limit compare estimates recently calculated for Sardinia Euregio Meuse–Rhine (EMR) sites. We find utility method, shows inconsistency predictions EMR site, indicates that require further improvement.