Paik-1

Search for Gravitational Waves

Ho Jung PaikUniversity of Maryland

and Seoul National University

January 12, 2006Seoul, Korea

KIAS-SNU Physics Winter Camp

Paik-2

Gravitational Waves

,0),(1

2

2

22

BEtc

Tc

GG

4

π8Field equation in General Relativity:

A wave equation, in the weak-field limit.

hghtc

,01

2

2

22

Transverse, spin 1

EM wave: Gravitational wave:

Transverse, spin 2

Paik-3

Gravitational Wave Detection

Joseph Weber (c1960)

A gravitational wave will deposit energy into an elastic solid. (Weber, 1959)

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Resonant-Mass Detector 1

)(

)(

)(

)(

2221

1211

I

u

ZZ

ZZ

V

f

22m

1221

ZM

ZZ

• Antenna Transducer Amplifier

• Transducer is characterized by an impedance matrix.

• Electromechanical energy coupling:

f() u() I() V()ijZ

Paik-5

Resonant-Mass Detector 2

• Condition to detect a GW pulse with strength h:

2

2

π

2 S

SNB

a

aa

22S2

TkQ

TkDhM B

• Optimal strategy:

noise. thermal thereduce toneeded is largeA

2 , 2

Na

aBN

S

S

S

T

Q

TkE

Signal Antenna noise Amplifier noise Thermal Wideband Backaction

Paik-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)1/2 can be added to increase S further.

Energy transfer time: (/a) (M/m)1/4

Paik-7

S/C Inductive Transducer

MOUNTING FLANGE

ANTENNA

TEST MASS

DC SQUID

CIRCUIT BOARD

AIR FILTER

1.0~01.0

)2/(20

02

dm

AB

Paik-8

ALLEGRO

4-K antenna at LSUwith a superconducting inductive transducer

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AURIGA

Best result obtained: h < 5 x 10-21 Hz-1/2 within ~100 Hz band

100-mK antenna in Italy with a capactive transducer coupled to a dc SQUID

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ExplorerSwitzerland

Allegro USA NiobeAustralia

Nautilus, italy

Auriga, Italy

Resonant Bar Detectors

Paik-11

Network of Resonant Bars

Allegro Explorer Auriga

Nautilus

NiobeIGEC Network

Paik-12

Rate(y –1)

Search threshold h

h ~ 2 10-18 ~ 0.02 M⊙ converted @ 10 kpc

• Upper limit on the rate of gravitational waves bursts from the Galactic Center (1997-2000)

The area above the blue curve is excluded with a coverage > 90%

P. Astone, et al. PRD 68 (2003) 022001

IGEC Coincidence Search

• No evidence for gravity wave bursts was found.

Paik-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)

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Resonant Spheres

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

MiniGrailThe Netherlands

SchenbergBrazil

Paik-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

Paik-16

LIGO Hardware

6-W Nd:YAG laser

Fused silica mirror

Paik-17

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

Paik-20

Network of Interferometers

LIGO

detection confidence

GEO VirgoTAMA

AIGO?locate the sourcesdecompose the polarization of

gravitational waves

Paik-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.

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Promising Source: Compact Binaries

Paik-23

Matched Filtering

“chirps”

NS–NS: waveforms are well described

BH–BH: need better waveforms

Search: matched templates

Paik-24

Advanced LIGO

Active Seismic

Multiple Suspensions

Improved Optics

Higher Power Laser

Paik-25

Sensitivity Improvement

RateImprovement ~

104

narrow band optical

configuration

2008 +

Paik-26

Gravitational Waves in Space

Three spacecraft form an equilateral triangle with armlength of 5 million km

LISA 2012 +

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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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• 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.

LISA Spacecraft

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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 !!