Direct Measurement of the Acceleration of the Universe using 0.1Hz Band Laser Interferometer Gravitational Wave Antenna in Space

It may be possible to construct a laser interferometer gravitational wave antenna in space with $h_{rms}\sim 10^{-27}$ at $ f\sim 0.1Hz$ in this century. We show possible specification of this antenna which we call DECIGO. Using this antenna we show that 1) $\sim 10^5$ chirp signals of coalescing binary neutron stars per year may be detected with S/N $\sim 10^4$. 2) The time variation of the scale factor of our universe may be determined for ten years observation of binary neutron stars so that we can directly measure the acceleration of the universe. 3) the stochastic gravitational waves of order $\Omega_{GW}\gsim 10^{-20}$ predicted by the inflationary universe paradigm may be detected by correlation analysis for which effects of the recent cosmic acceleration would become highly important.