Mechanical Long Baseline Differential Gradiometers as Low Frequency Gravitational Wave Detectors

TL;DR

This paper introduces a novel mechanical differential gradiometer designed to detect low-frequency gravitational waves in the 0.05 to 1 Hz range, filling a gap between space-based and ground-based detectors.

Contribution

It proposes a new detection principle using a vertically operated system with a counterweight and suspended mass, enhancing gravitational force measurement without increasing system inertia.

Findings

The design extends the detectable signal amplitude proportional to the ratio L/D.

The configuration builds on recent tiltmeters and interferometric read-out technologies.

Expected sensitivity is analyzed based on proposed parameters and current technology.

Abstract

We present a new differential mechanical gradiometer for the detection of low-frequency Gravitational Waves. The frequency range is 0.05 to 1 Hz, a frequency gap not covered either by future space-based detectors such as LISA or by ground-based observatories such as Einstein Telescope or Cosmic Explorer. The proposed detection principle is similar to antennas based on torsion pendulums but solves the problem of physical confinement of these antennas by operating vertically and by having a counterweight at one end of each bar and a mass suspended from a long wire at the other. With this configuration, we enlarge the gravitational force acting on the system \textit{without} changing the moment of inertia of the system, so that we move from a signal $\Delta \theta$ of the order of $\Delta \theta = h$, where h is the amplitude of the gravitational wave, to a signal of the order $\Delta \theta = h\frac{L}{D}$, where D is the length of the arm and L is the length of the wire suspending the test mass. This configuration is a further evolution of the recent development of tiltmeters and balances with double suspended arms and interferometric read-out, where the main working principles are already tested. The expected sensitivity will be discussed with respect to the proposed parameters and the present technology.