Determination of the equation of the state of the Universe using ~ 0.1 Hz Gravitational Wave Detectors

We show that ten(one) years operation of the ultimate DECIGO (DECihertz Interferometer Gravitational wave Observatory) can determine the cosmic equation of the state with such accuracy that 0.06%(3%), 0.08%(4%) and 0.06%(3%) for ${\mathrm{\Omega }}_m$, ${\mathrm{\Omega }}_w$ and $w$, respectively. In more realistic case of practical DECIGO or BBO (Big Bang Observer), $w$ will be determined within $\sim 10$ by ten years observation assuming the flat universe model. Hence, the DECIGO or BBO will give an independent determination of the cosmic equation of the state.