Transcript CERCA - LIGO

What can gravitational waves do to
probe early cosmology?
WMAP 2003
Barry C. Barish
Caltech
“Kavli-CERCA Conference
on the Future of Cosmology”
Case Western Reserve University
October 10-12, 2003
LIGO-G030556-00-M
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Signals from the Early Universe
The smaller the cross-section, the earlier the particle
decouples
 Photons:
T = 0.2 eV
t = 300,000 yrs
 Neutrinos:
T = 1 MeV
t ~ 1 sec
 Gravitons:
T = 1019 GeV
t ~ 10-43 sec
Cosmic
Microwave
background
WMAP 2003
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GW Stochastic Backgrounds
Primordial stochastic
backgrounds: relic GWs
produced in the early
Universe
 Cosmology
 Unique laboratory for
fundamental physics at
very high energy
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GW Stochastic Backgrounds
Astrophysically generated
stochastic backgrounds
(foregrounds): incoherent
superposition of GWs from
large populations of
astrophysical sources
 Populations of compact
object in our galaxy and at
high redshift
 3D distribution of sources
 Star formation history
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The Gravitational Wave Signal

The spectrum:
 The characteristic amplitude
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What we know
limits on primordial backgrounds
The fluctuation of the temperature of
the cosmic microwave background
White dwarf and neutron
radiation. A strong background of
star binary system has
gravitational
atare
very
long
ms waves
pulsars
fantastic
second clock, the orbital
wavelengths
produces
a stochastic
clocks!
Stability
places
period! Change in orbital
redshift
on
the
frequencies
of 4the
The primordial
abundance
of
He
limit on
gravitational
waves
period can be computed
in
photons
of
the
2.7
K
radiation,
and
is exponentially
sensitive
tothe
thepulsar
passing
between
GR, simplifying fitting.
therefore
aand
fluctuation
in This
theirsets
freeze-out
temperature.
us.
Integrating
for one
Gives limit from 10-11temperature
to
limit on the
number
relic
year
givesof
limit
at f ~ 4.4
4.4 10-9 Hz
gravitons. 10-9 Hz
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-
Theoretical Predictions
Some theoretical “prediction”
Strings
Super-string
Inflation
Phase transition
Maggiore 2000
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Expected Signal Strength
log Omega(f)
Nucleosynthesis
-5
?
-10
Slow-roll inflation
-15
-6
-3
0
3
6
log f
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Detection
of
Gravitational Waves
Gravitational Wave
Astrophysical
Source
Terrestrial detectors
Detectors
in space
Virgo, LIGO, TAMA, GEO
AIGO
LISA
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Astrophysics Sources
frequency range
 Gravitational Waves can be studied over ~10
orders of magnitude in frequency

terrestrial + space
Audio band
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Interferometer Concept
 Arms in LIGO are 4km
 Laser used to
measure relative  Measure difference in
lengths of two
length to one part in
orthogonal arms
1021 or 10-18 meters
…causing the
interference
pattern to change
at the photodiode
As a wave
Suspended
passes, the
Masses
arm
lengths
change in
different
ways….
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International Network
 Network
Required
for:
» Detection
Confidence
» Waveform
Extraction
» Direction by
Triangulation
TAMA300
Tokyo
LIGO
Hanford, WA
LIGO
Livingston, LA
GEO600
Hanover Germany
VIRGO
Pisa, Italy
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+ “Bar Detectors” : Italy, Switzerland, Louisiana, Australia
Stochastic Background Signal
auto-correlation
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Overlap Reduction Function
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Simultaneous Detection
LIGO
Hanford
Observatory
MIT
Caltech
Livingston
Observatory
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LIGO Livingston Observatory
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LIGO Hanford Observatory
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What Limits LIGO Sensitivity?

Seismic noise limits low
frequencies

Thermal Noise limits
middle frequencies

Quantum nature of light
(Shot Noise) limits high
frequencies

Technical issues alignment, electronics,
acoustics, etc limit us
before we reach these
design goals
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LIGO Sensitivity
Livingston 4km Interferometer
First Science
Run
17 days - Sept 02
May 01
Jan 03
Second Science
Run
59 days - April 03
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Signals from the Early Universe
 Strength specified by ratio of energy density in GWs to
total energy density needed to close the universe:
ΩGW (f) 

1
ρcritical
dρGW
d(lnf)
Detect by cross-correlating output of two GW
detectors:
First LIGO Science Data
Hanford - Livingston
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Limits: Stochastic Search
Interferometer
Pair
90% CL Upper Limit
Tobs
LHO 4km-LLO 4km
WGW (40Hz - 314 Hz) < 72.4
62.3 hrs
LHO 2km-LLO 4km
WGW (40Hz - 314 Hz) < 23
61.0 hrs
 Non-negligible LHO 4km-2km (H1-H2) instrumental crosscorrelation; currently being investigated.
 Previous best upper limits:
» Garching-Glasgow interferometers :
ΩGW (f)  3 10 5
» EXPLORER-NAUTILUS (cryogenic bars): ΩGW (907Hz)  60
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Gravitational Waves
from the Early Universe
results
projected
E7
S1
S2
LIGO
Adv LIGO
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Interferometers in Space
The Laser
Interferometer
Space Antenna
(LISA)
 The center of the triangle formation will be in the
ecliptic plane
 1 AU from the Sun and 20 degrees behind the Earth.
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LISA: Sources and Sensitivity
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LISA: Astrophysical Backgrounds
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Detecting the Anisotropy
(1) Break-up the yrs long data set in
short (say a few hrs long) chunks
(2) Construct the new signal
(3) Search for peaks in S(t):
The LISA motion is periodic
S m observable
is the
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Instrument’s sensitivity
LIGO-I
Advanced LIGO
3rd generation
LISA
Correlation of 2 LISA’s
Slow-roll inflation
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Sensitivity
Primordial Stochastic Background
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Stochastic Background
Astrophysical Foregrounds
• White-dwarf binary systems (galactic and
extra-galactic) (Hils et al, 1990; Schneider et al, 2001)
• Neutron star binary systems (galactic and
extra-galactic) (Schneider et al, 2001)
• Rotating neutron stars (galactic and extragalactic) (Giazzotto et al, 1997; Regimbau and de Freitas
Pacheco, 2002)
• Solar mass compact objects orbiting a
massive black hole (extra-galactic) (Phinney 2002)
• Super-massive black hole binaries (extragalactic) (Rajagopal and Romani, 1995)
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Astrophysical Signals
Limit Sensitivity for Primordial
Sources
Extragalactic
WD-WD
10-10
Extragalactic
NS-NS
WD-WD
LISA - 1yr
10-16
10-13
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Ultimate GW Stochastic Probes
log Omega(f)
3rd generation sensitivity limit (1yr)
?
-11
WD-WD
-12
NS-NS
-13
CLEAN
LISA sensitivity limit (1yr)
-14
NS
BH-MBH
CORRUPTED
-15
-16
-6
-5
-4
-3
-2
-1
0
1
2
3 log f
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Future experiments in the
“gap” (?)
10-18
MBH-MBH
coalescences
h
Earth
90°
LIGO
10-20
SN
90°
Sun
10-22
NS
LISA
Unresolved
Binaries
10-24
LISA II
10-26
10-7
A. Vecchio
10-5
10-3
10-1
101
103
Frequency [Hz]
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Conclusions

Primordial Gravitational Wave Stochastic
Background is potentially a powerful probe of
early cosmology

Present/planned earth/space-based
interferometers will begin to probe the
sensitivity regime of interest.
 They will either set limits constraining early
cosmology or detect the stochastic
background

They are ultimately limited to ~10-11 and 10-13
in energy density

A future short arm space probe could probe
the gap (0.1 – 1 Hz region looks cleanest)
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