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Search for Gravitational Waves

KIAS-SNU Physics Winter Camp. Search for Gravitational Waves. Ho Jung Paik University of Maryland and Seoul National University January 12, 2006 Seoul, Korea. Gravitational Waves. Field equation in General Relativity:.  A wave equation, in the weak-field limit. EM wave:.

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Search for Gravitational Waves

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  1. KIAS-SNU Physics Winter Camp Search for Gravitational Waves Ho Jung Paik University of Maryland and Seoul National University January 12, 2006 Seoul, Korea

  2. Gravitational Waves Field equation in General Relativity: A wave equation, in the weak-field limit. EM wave: Gravitational wave: Transverse, spin 1 Transverse, spin 2

  3. Gravitational Wave Detection A gravitational wave will deposit energy into an elastic solid. (Weber, 1959) Joseph Weber (c1960)

  4. Resonant-Mass Detector 1 • Antenna  Transducer  Amplifier • Transducer is characterized by an impedance matrix. f() u() I() V() • Electromechanical energy coupling:

  5. Resonant-Mass Detector 2 • Condition to detect a GW pulse with strength h: • Signal Antenna noise Amplifier noise • ThermalWidebandBackaction • Optimal strategy:

  6. Resonant Transducer • To get large , a resonant mass is attached to the antenna (Paik, 1972) •  Displacement gain: • (M/m)1/2 102 •  Energy transfer time: •   (/a) (M/m)1/2 • An additional resonant mass with  =(Mm)1/2can be added to increase S further. •  Energy transfer time: •   (/a) (M/m)1/4

  7. S/C Inductive Transducer

  8. ALLEGRO 4-K antenna at LSU with a superconducting inductive transducer

  9. AURIGA 100-mK antenna in Italy with a capactive transducer coupled to a dc SQUID Best result obtained: h < 5 x 10-21 Hz-1/2 within ~100 Hz band

  10. Resonant Bar Detectors Auriga, Italy Allegro USA Niobe Australia Nautilus, italy Explorer Switzerland

  11. Network of Resonant Bars Auriga Allegro Explorer Nautilus Niobe IGEC Network

  12. IGEC Coincidence Search • Upper limit on the rateof gravitational waves bursts from theGalactic Center (1997-2000) P. Astone, et al. PRD 68 (2003) 022001 Rate (y –1) The area above the blue curve is excluded with a coverage > 90% Search thresholdh h~ 2 10-18 ~ 0.02 M⊙ converted @ 10 kpc • No evidence for gravity wave bursts was found.

  13. Spherical Antenna • Sphere is omni-directional. • By detecting its 5 quadrupole modes, the source direction (, ) and wave polarization (h+, h) can be determined. (Wagoner & Paik, 1976) • 6 radial transducers on truncated icosahedral configuration maintains “spherical” symmetry. • (Johnson & Merkowitz, 1993) •  TIGA • (Truncated Icosahedral • Gravitational Antenna)

  14. Resonant Spheres • Much larger cross-section than a bar of the same resonance frequency (up to 70 x) MiniGrail The Netherlands Schenberg Brazil

  15. Interferometer Concept • Laser used to measure relative lengths of two orthogonal arms • Arm lengths in LIGO are 4 km • Measure difference in length to 10-19 m

  16. LIGO Hardware Fused silica mirror 6-W Nd:YAG laser

  17. Seismic noise limits at low frequencies. Atomic vibrations (thermal noise) inside the components limit at mid frequencies. Quantum nature of light (shot noise) limits at high frequencies. Limiting Noise Sources

  18. Evolution of LIGO Sensitivity

  19. Interferometer Detectors TAMA Japan 300m LIGO Louisiana 4000m Virgo Italy 3000m GEO Germany 600m LIGO Washington 2000m & 4000m

  20. Network of Interferometers Virgo LIGO GEO TAMA AIGO? decompose the polarization of gravitational waves detection confidence locate the sources

  21. LIGO Science Has Begun S1 run: 17 days (Aug - Sep 2002) Primarily methods papers Four astrophysical searches published (Phys. Rev. D 69, 2004): Inspiraling neutron stars, bursts, known pulsar (J1939+2134) with GEO,stochastic background S2 run:59 days (Feb - April 2003) Analyses are mostly complete. S3 run: 70 days (Oct 2003 – Jan 2004) Analysis is in full swing.

  22. Promising Source: Compact Binaries

  23. Matched Filtering “chirps” NS–NS:waveforms are well described BH–BH: need better waveforms Search: matched templates

  24. Advanced LIGO Active Seismic Multiple Suspensions Improved Optics Higher Power Laser

  25. Sensitivity Improvement 2008 + Rate Improvement ~ 104 narrow band optical configuration

  26. Gravitational Waves in Space LISA 2012 + Three spacecraft form an equilateral triangle with armlength of 5 million km

  27. LISA Accelerometer The position of a reference mass is sensed by a capacitor bridge and used for drag-free control.

  28. LISA Spacecraft • Y-shaped payload has two identical optical assemblies with transmit/receive telescopes. • The inertial sensor consists of a free-falling proof mass inside a reference housing.

  29. Sources for LISA

  30. LISA and LIGO

  31. Status of Interferometers • Sensitivity toward gravitational wave detection is improving on many fronts. • Improved limits are being set for all major sources -- binary inspirals, periodic sources, burst sources, and stochastic background. • Data exchange and joint data analysis between detector groups is improving ability to make detections. • Need specific waveforms to improve search sensitivities! • Hopefully, detections will be made soon !!

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