Abstract:
The Einstein Telescope (ET) is a proposed third-generation gravitational-wave detector featuring a unique triangular geometry consisting of three co-located interferometers with arm lengths of 10 km. The triangular configuration yields important assets: from more high-quality observation time to the "null stream", a linear combination of the three detector outputs that contains no gravitational wave signal. This talk reviews how the triangular design enables several powerful analysis techniques for third-generation gravitational-wave astronomy. Firstly, the null stream provides signal-free data for unbiased noise characterization, critical when detection rates reach hundreds to thousands of events per day. Secondly, it enables glitch mitigation—removing instrumental noise transients without contaminating astrophysical signals. Thirdly, it supports effective discrimination of signals from noise, enabling up to 82% more detections. Finally, it enables detector calibration independent of waveform models, opening opportunities for precision science. The null stream thus represents a key advantage of the triangular ET design, with important implications for next-generation detector design choices.