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Abstract

Among third-generation ground-based gravitational-wave detectors proposed for
the next decade, Einstein Telescope provides a unique kind of null stream
$\unicode{x2014}$ the signal-free linear combination of data $\unicode{x2014}$
that enables otherwise inaccessible tests of the noise models. We project and
showcase challenges in modeling the noise in the 2030-s and how it will affect
the performance of third-generation detectors. We find that the null stream of
Einstein Telescope is capable of entirely eliminating transient detector
glitches that are known to limit current gravitational-wave searches. The
techniques we discuss are computationally efficient and do not require a-priori
knowledge about glitch models. Furthermore, we show how the null stream can be
used to provide an unbiased estimation of the noise power spectrum necessary
for online and offline data analyses even with multiple loud signals in band.
We overview other approaches to utilizing the null stream. Finally, we comment
on the limitations and future challenges of null stream analyses for Einstein
Telescope and arbitrary detector networks.