Formalism for power spectral density estimation for non-identical and correlated noise using the null channel in Einstein Telescope

Understand

Several proposed gravitational wave interferometers have a triangular configuration, such as the Einstein Telescope and the Laser Interferometer Space Antenna.

• For such a configuration one can construct a unique null channel insensitive to gravitational waves from all directions.
• We expand on earlier work and describe how to use the null channel formalism to estimate the power spectral density for the Einstein Telescope interferometers with non-identical as well as correlated noise sources.
• The formalism is illustrated with two examples in the context of the Einstein Telescope, with increasing degrees of complexity and realism.