Signal Space in the Triangular Network of Einstein Telescope

Understand

The proposed third-generation gravitational-wave detectors Einstein Telescope will have a triangular design that consists of three colocated interferometers.

• Summing the strain outputs from the three interferometers will cancel any gravitational-wave signal and the resultant signal-free stream is known as null stream.
• The null stream is in a fixed subspace of the observation space of Einstein telescope where no gravitational-wave signal can exist.
• In this paper, we establish the decomposition of the observation space of Einstein Telescope into the signal space that contains all possible gravitational-wave signals and the null space that contains the null stream.