Search for Gravitational Waves

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KIAS-SNU Physics Winter Camp
Search for Gravitational Waves
Ho Jung Paik University of Maryland and Seoul
National University January 12, 2006 Seoul,
Korea
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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
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Gravitational Wave Detection
A gravitational wave will deposit energy into an
elastic solid. (Weber, 1959)
Joseph Weber (c1960)
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Resonant-Mass Detector 1

• Antenna ? Transducer ? Amplifier
• Transducer is characterized by an impedance
  matrix.

f(?)
u(?)
I(?)
V(?)

• Electromechanical energy coupling

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Resonant-Mass Detector 2

• Condition to detect a GW pulse with strength h

Signal Antenna noise Amplifier noise
Thermal Wideband Backaction

• Optimal strategy

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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)1/2 can
  be added to increase ??S further.
• ? Energy transfer time
• ? ? (?/?a) (M/m)1/4

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S/C Inductive Transducer
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ALLEGRO
4-K antenna at LSU with a superconducting
inductive transducer
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AURIGA
100-mK antenna in Italy with a capactive
transducer coupled to a dc SQUID
Best result obtained h lt 5 x 10-21 Hz-1/2
within 100 Hz band
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Resonant Bar Detectors
Auriga, Italy
Allegro USA
Niobe Australia
Nautilus, italy
Explorer Switzerland
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Network of Resonant Bars
Auriga
Allegro
Explorer
Nautilus
Niobe
IGEC Network
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IGEC Coincidence Search

• Upper limit on the rate of gravitational waves
  bursts from the Galactic 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 gt 90
Search threshold h
h 2 ?10-18
0.02 M? converted _at_ 10 kpc

• No evidence for gravity wave bursts was found.

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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)

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Resonant Spheres

• Much larger cross-section than a bar of the same
  resonance frequency (up to 70 x)

MiniGrail The Netherlands
Schenberg Brazil
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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

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LIGO Hardware
Fused silica mirror
6-W NdYAG laser
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Limiting Noise Sources

• 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.

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Evolution of LIGO Sensitivity
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Interferometer Detectors
LIGO Louisiana 4000m
TAMA Japan 300m
Virgo Italy 3000m
GEO Germany 600m
LIGO Washington 2000m 4000m
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Network of Interferometers
Virgo
LIGO
GEO
TAMA
AIGO?
decompose the polarization of gravitational waves

detection confidence
locate the sources
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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
  (J19392134) 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.

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Promising Source Compact Binaries
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Matched Filtering
chirps
NSNS waveforms are well described BHBH need
better waveforms Search matched templates
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Advanced LIGO
Multiple Suspensions

• Active Seismic

Improved Optics
Higher Power Laser
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Sensitivity Improvement
2008
Rate Improvement 104
narrow band optical configuration
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Gravitational Waves in Space
LISA
2012
Three spacecraft form an equilateral triangle
with armlength of 5 million km
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LISA Accelerometer
The position of a reference mass is sensed by a
capacitor bridge and used for drag-free control.
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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.

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Sources for LISA
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LISA and LIGO
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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 !!