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DECIGO – Japanese Space Gravitational Wave Detector

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  1. DECIGO – Japanese Space Gravitational Wave Detector International Workshop on GPS Meteorology January 17, 2003 @ Tsukuba Center for Institutes Seiji Kawamura* and DECIGO-WG (*) National Astronomical Observatory of Japan

  2. What is Gravitational Wave? • Predicted by A. Einstein in the general relativity • Not yet detected directly • Emitted by accelerating masses • Causing a time-variant tidal strain in space • Propagating with the speed of light

  3. Detection of Gravitational Waves Using Laser Interferometer

  4. Longer arm gives larger signals! Mirror Shrinking More Shrinking Mirror Extending Laser Mirror Photodetector Extending More Laser Mirror Photodetector

  5. GEO (600m) TAMA (300m) LIGO (4km) LCGT (3km) VIRGO (3km) LIGO (4km) AIGO (?km) Large-scale GW Detectorsin the World

  6. - 1 3 1 0 F e b . 1 9 9 9 S e p . 1 9 9 9 1 0 - 1 5 S e p . 2 0 0 0 1 0 - 1 7 J u n . 2 0 0 1 1 0 - 1 9 A u g . 2 0 0 2 1 0 - 2 1 1 0 1 0 0 1 k 1 0 k 1 0 0 k F r e q u e n c y [ H z ] Achievements of TAMA300 2000: World-best sensitivity obtained 2001: World-longest 1000 hours of data obtained

  7. Laser Interferometer in Space • Signal increased - Due to longer interaction between GW and light - Cancellation of signals at higher frequencies • Noise reduced - Lower seismic noise and gravity gradient noise Sensitivity improved at lower frequencies

  8. Laser Interferometer Space Antenna • Joint Project by NASA and ESA • Aiming at 0.1mHz - 100mHz • To be launched in 2001 LISA

  9. 10-18 10-20 10-22 10-24 Gap between Terrestrial Detectors and LISA LISA Terrestrial Detectors Strain [Hz-1/2] (e.g. LCGT) Gap 10-4 102 100 104 10-2 Frequency [Hz]

  10. Importance of Bridgingthe 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 • Completely new sources could be detected • Completely new science could be obtained

  11. GWs from Inspirals

  12. 10-18 LISA 10-20 Terrestrial Detectors Strain [Hz-1/2] (e.g. LCGT) DECIGO 10-22 (Sensitivity: Arbitrary) 10-24 10-4 102 100 104 10-2 Frequency [Hz] What is DECIGO? • Deci-hertz Interferometer Gravitational Wave Observatory • Space Antenna with shorter arm length

  13. 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

  14. 10-18 10-19 10-20 10-21 102 100 10-4 10-2 Relationship between Sensitivity and Arm Length x100 f1 f-2 LISA Strain [Hz-1/2] DECIGO Force Noise: f0 f0:1/L (Arm Length: f0 XFN/L∝1/L 1/100 of LISA) x100 Shot Noise (f<f0): XSN/L∝P-1/2/L∝(L-2) -1/2/L=L/L Frequency [Hz]

  15. Advantages of DECIGO No confusion limiting noise above 0.1Hz (From the LISA report)

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

  17. 10-18 10-20 10-22 10-24 10-4 102 100 104 10-2 10-26 Ultimate Sensitivity of DECIGO DECIGO (LISA Technology L=5×107m) LISA Terrestrial Detectors (e.g. LCGT) Strain [Hz-1/2] Ultimate DECIGO × 1000 (Necessary for acceleration measurement) Ultimate DECIGO (Quantum noise limited M=100kg, L=5×108m) Frequency [Hz]

  18. 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.

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

  20. 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

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

  22. 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

  23. 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. • R&D experiments will be started very soon.