Upper Limit on Gravitational Wave Backgrounds at 0.2 Hz with Torsion-bar Antenna

TL;DR

This paper reports the first upper limit on gravitational wave backgrounds at 0.2 Hz using a torsion-bar antenna, bridging a gap between existing GW frequency bands and demonstrating the device's potential.

Contribution

We developed a small-scale torsion-bar antenna and established the first upper limit on GW energy density at 0.2 Hz, expanding the frequency range of GW searches.

Findings

Set an upper limit of a_{gw}(f) < 4.3 imes 10^{17} at 0.2 Hz

Demonstrated the capability of a torsion-bar antenna for low-frequency GW detection

Bridged the gap between LIGO and Cassini GW frequency bands

Abstract

We present the first upper limit on gravitational wave (GW) backgrounds at an unexplored frequency of 0.2 Hz using a torsion-bar antenna (TOBA). A TOBA was proposed to search for low-frequency GWs. We have developed a small-scaled TOBA and successfully found {\Omega}gw(f) < 4.3 \times 1017 at 0.2 Hz as demonstration of the TOBA's capabilities, where {\Omega}gw (f) is the GW energy density per logarithmic frequency interval in units of the closure density. Our result is the first nonintegrated limit to bridge the gap between the LIGO band (around 100 Hz) and the Cassini band (10-6 - 10-4 Hz).