Wataru Kokuyama

Upper limit on gravitational wave backgrounds at 0.2 Hz with a torsion-bar antenna.

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 Ω(gw)(f)<4.3×10(17) at 0.2 Hz as demonstration of the TOBAs capabilities, where Ω(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).

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

We have set a new upper limit on the stochastic gravitational-wave background using two prototype torsion-bar antennas (TOBAs). A 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

New limit on Lorentz violation using a double-pass optical ring cavity.

{\mathrm{\ensuremath{\Omega}}}_{\mathrm{gw}}{h}_{0}^{2}l1.9\ifmmode\times\else\texttimes\fi{}{10}^{17}

Simple iodine reference at 1064 nm for absolute laser frequency determination in space applications

at 0.035--0.830 Hz, where

Simple digital phase-measuring algorithm for low-noise heterodyne interferometry

{h}_{0}

Search for a Stochastic Gravitational-wave Background with Torsion-bar Antennas

is the Hubble constant in units of

Higher order test of Lorentz invariance with an optical ring cavity

100\text{ }\text{ }\mathrm{km}/\mathrm{s}/\mathrm{Mpc}

Time-domain phase noise measurement in the optical frequency region

and

An enhanced primary shock calibration procedure to reduce the zero shift effect of piezoelectric transducers by using a virtual amplifier

{\mathrm{\ensuremath{\Omega}}}_{\mathrm{gw}}

Shock Calibration with Zero Shift Using a Digital Filter Technique

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.