Search for a Stochastic Gravitational-wave Background using a pair of Torsion-bar Antennas

Understand

We have set a new upper limit on the stochastic gravitational wave background (SGWB) using two prototype Torsion-bar Antennas (TOBAs).

• TOBA is a low-frequency gravitational-wave detector with bar-shaped test masses rotated by the tidal force of gravitational waves.
• As a result of simultaneous 7-hour observations with TOBAs in Tokyo and Kyoto in Japan, our upper limit with a confidence level of 95% is $\Omega_{\rm gw}h_0^2 < 1.9 \times 10^{17}$ at 0.035 - 0.830 Hz, where $h_{0}$ is the Hubble constant in units of 100 km/s/Mpc and $\Omega_{\rm gw}$ is the gravitational wave energy density per logarithmic frequency interval in units of the closure density.
• We successfully updated the upper limit and extended the explored frequency band.