1. Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) 7th Gravitational Wave Data Analysis Workshop December 17, 2002 @ International Institute for Advanced Studies, Japan Seiji Kawamura National Astronomical Observatory of Japan

2. Contents 1.Introduction 2.What is DECIGO? 3.Science obtained by DECIGO 4.Sensitivity of DECIGO 5.Current Status of DECIGO 6.Summary

3. Gap between Terrestrial Detectors and LISA 10 -18 10 -24 10 -22 10 -20 10 -4 10 4 10 2 10 0 10 -2 Frequency [Hz] Strain [Hz -1/2 ] LISA Terrestrial Detectors (e.g. LCGT) Gap

4. Importance of Bridging the Gap New window brings new science! Observe inspiral sources that have moved above the LISA band Observe inspiral sources that have not yet moved into the ground-based detector band Cosmological background could be detected  Seto’s talk Completely new sources could be detected Completely new science could be obtained  Seto’s talk

5. What is DECIGO? Deci-hertz Interferometer Gravitational Wave Observatory Space Antenna with shorter arm length 10 -18 10 -24 10 -22 10 -20 10 -4 10 4 10 2 10 0 10 -2 Frequency [Hz] Strain [Hz -1/2 ] LISA Terrestrial Detectors (e.g. LCGT) DECIGO (Sensitivity: Arbitrary)

6. DECIGO Named by T. Nakamura in the PRL paper by N. Seto, S. Kawamura, and T. Nakamura Potential candidate for the future Japanese space GW antenna Study of DECIGO just started; still primitive

7. Relationship between Sensitivity and Arm Length 10 -18 10 -21 10 -19 10 -20 Frequency [Hz] Strain [Hz -1/2 ] LISA 10 -4 10 2 10 0 10 -2 DECIGO Shot Noise (f<f 0 ): X SN /L ∝ P -1/2 /L ∝ (L -2 ) -1/2 /L=L/L (Arm Length: x100 f0f0 f0f0 1/100 of LISA) Force Noise: x100 X FN /L ∝ 1/L f 0 :1/L f1f1 f -2

8. Advantages of DECIGO No confusion limiting noise above 0.1Hz  Seto’s Talk (From the LISA report)

9. Acceleration of Expansion of the Universe  Seto’s Talk NS-NS (z ～ 1) GW DECIGO Output Expansion ＋ Acceleration? Time Strain Template (No Acceleration) Real Signal ? Phase Delay ～ 1sec (10 years) Seto, Kawamura, Nakamura, PRL 87, 221103 (2001)

10. Ultimate Sensitivity of DECIGO Frequency [Hz] 10 -4 10 4 10 2 10 0 10 -2 Strain [Hz -1/2 ] LISA Terrestrial Detectors (e.g. LCGT) Ultimate DECIGO 10 -18 10 -24 10 -22 10 -20 10 -26 M=100kg, L=5×10 8 m) (Quantum noise limited DECIGO (LISA Technology L=5×10 7 m) Ultimate DECIGO × 1000 (Necessary for acceleration measurement)

11. In the Paper, we said… The ultimate sensitivity of a space antenna in the far future could be, however, 3  10 -27 around 0.1 Hz in terms of strain, assuming the quantum limit sensitivity for a 100 kg mass and an arm length of 1/10 of LISA. We name this detector DECIGO. This requires an enormous amount of effective laser power, and also requires that the other noise sources, such as gravity gradient noise, thermal noise, practical noise, etc. should be all suppressed below the quantum noise. Here we assume that such an antenna may be available by the end of this century.

12. Necessary Technologies for DECIGO Solar Radiation Deflection of Light Gravity Gradient Three Satellite Formation Flight Drag-free Satellite Heterodyne Detection Reflection with phase- locking

13. How to Improve Sensitivity? Increase effective power - Increase the laser power - Increase the diameter of mirror Use shorter wavelength? Reduce other sensing noise Reduce force noise

14. DECIGO Working Group Convened in 2002 as one of WGs to study the future project candidates for NAOJ 1 st Meeting held on May 9, 2002 83 members currently involved R&D experiments to be started very soon

15. Two R&D Experiments to be Started Very Soon Collaboration work between NASA- Goddard (LISA) and NAOJ (DECIGO) on ground testing of space interferometry Constructing a measurement system for Earth environmental monitoring by CRL, Niigata Univ., and NAOJ

16. Conclusions It is important to bridge the gap between terrestrial detectors and LISA. DECIGO is a candidate for the Japanese space GW antenna. DECIGO-WG has just started investigating the possibility. Two R&D experiments will be started very soon.