1 Determination of the equation of state of the universe using 0.1Hz Gravitational Wave Antenna Takashi Nakamura and Ryuichi Takahashi Dept. Phys. Kyoto Univ Dec.15.GWDAW9 Prog.Theor.Phys in press

2 Dark energy is the most important and most difficult problem in physics in the 21 st century so that many independent observations and experiments are indispensable. At first the optical astronomy took part in the game using the type Ia supernova Then CMB took part in the game by WMAP Very recently GRB has taken part in the game. In future why not gravitational wave!!

3 Ghirlanda et al (2004) ? Peak energy of the spectra to total jet gamma ray energy relation

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5 GRBs with known z

6 Swift was launched 2004 Nov 20 →more data will be available

7 In 2001 we considered what we can do using 0.1 hertz laser interferometer ( Seto, Kawamura and TN : PRL )

8 Our Point and Strategy Consider the ultimate possible detector in the sprit of necessity is the mother of the invention We call the detector DECIGO( DECi hertz laser Interferometer Gravitational wave Observatory) Consider the coalescing binary neutron stars at z=1. Observe them one year before the final merging

9 Time delay of chirp signal due to the acceleration of the universe can be measured

10 Matched Filter Analysis Using Ultimate DECIGO

11 Punch Point of Ultimate DECIGO a)100,000 Mass of neutron stars, Black Hole will give us mass function of NS and BH b)Direct measurement of Acceleration of the universe; Independent measurement of the curvature of the universe, independent information of EOS of the universe Today we discuss more details. c)Background gw predicted by inflation model up to can be measured. Completely independent information from MAP and PLANCK d) If the fundamental scale is Tev, then the redshifted GW at T=Tev is just 0.1Hz Band. We may see something. e) For near source, accurate time(0.01sec) and spatial position(10arcsec) of the coalescing binary neutron stars a week before the final merging (Takahashi and Nakamura at GWDAW8 and ApJ 596 (2003) 231)

12 discovery of new binary pulsar PSR J Coalescence rate 180/Myr/Galaxy although corrected factor 2 in 2004.

13 S/N will increase Expected event rate as a function of z

14 Accuracy of determination of Hubble parameter as a function of z.

15 Dependence of the accuracy on the observing time

16 Dependence of the accuracy on the mass of the binary

17 Equation of the state of the dark energy The angular position of the source is determined within a few arc seconds so that the host galaxy will be identified. Then the red shift z will be obtained.

18 The estimation error of cosmological parameters for general non-flat universe

19 The estimation error of cosmological parameters for flat universe

20 The estimation error of cosmological parameters for SNAP satellite case

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22 Conclusion 1) We showed that the ultimate DECIGO can determine the cosmological parameters comparable or better than SNAP. 2) This is completely independent determination of the property of the dark energy. 3) To determine more than 100,000 wave signals is a challenge for data analysis. 4) What we can do by 1000 times less sensitive practical DECIGO with ten years observations.

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25 After subtracting these binaries and possible other sources from the row data, we might observe the primordial gw background even if