Seismic Cross-coupling Noise in Torsion Pendulums

TL;DR

This paper investigates seismic cross-coupling noise in torsion pendulums used for gravitational wave detection, identifying transfer routes and proposing effective noise reduction methods validated through experiments.

Contribution

It systematically identifies seismic cross-coupling pathways in torsion pendulums and demonstrates practical reduction schemes with experimental validation.

Findings

Identified main routes of seismic cross-coupling in torsion pendulums.

Proposed and experimentally validated noise reduction schemes.

Established a fundamental approach to mitigate seismic noise for gravitational wave detection.

Abstract

Detection of low frequency gravitational waves around 0.1 Hz is one of the important targets for future gravitational wave observation. One of the main sources of the expected signals is gravi- tational waves from binary intermediate-mass black hole coalescences which is proposed as one of the formation scenarios of supermassive black holes. By using a torsion pendulum, which can have a resonance frequency of a few millihertz, such signals can be measured on the ground since its rotational motion can act as a free mass down to 0.01 Hz. However, sensitivity of a realistic tor- sion pendulum will suffer from torsional displacement noise introduced from translational ground motion in the main frequency band of interest. Such noise is called seismic cross-coupling noise and there have been little research on it. In this paper, systematic investigation is performed to identify routes of cross-coupling transfer for standard torsion pendulums. Based on the results this paper also proposes reduction schemes of cross-coupling noise, and they were demonstrated experimen- tally in agreement with theory. This result establishes a basic way to reduce seismic noise in torsion pendulums for the most significant coupling routes.