Searches for very high frequency gravitational waves
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Transcript of Searches for very high frequency gravitational waves
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Mike Cruise
University of Birmingham
Searches for very high frequency gravitational waves
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Signals from Neutron Stars
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Signals from SMBH’s
LIGO , Virgo, LISA or pulsar timing are most likely to make the first detections
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Why go to higher frequencies?
• Other branches of astronomy developed through mullti-frequency observations
• For frequencies >1 MHz– Cosmological signals from the Planck era.– KK mode oscillations in higher dimensions– EMW-plasma instabilities generate GW’s– Radiation from non-minimal coupling of the
EM and G fields
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Very High Frequency detectors?
• The best upper limit at 100 MHz by Akutsu and Kawamura of ~10-17 was with an interferometer
• But Interferometer sensitivity worsens as• Minimum detectable EM signal in a 1 Hz
bandwidth ~ 10-20 W• Maximum EMW power ~ 10’s of MW
• ratio of min detectable signal ~ 10-27
max available energy
21
E or B
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Pathways for coupling EM and Gravity
22
2 2 4
116
Gh T
c t c
F g g F
May contain EM Fields
Contain G potentials
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How does a GW interact with a static EM Field?
• De Logi and Mickelson (1977)
Graviton
Virtual Photon( Static Magnetic Field )
Photon
3
228
c
LGBSpin states of g, B and
For one incoming graviton per second
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What are the fluxes?
• Flux of photons is times the flux of gravitons
• EM Signal Power is
1
1622
2
hG
cFlux
22222
08
1cSinhKLBP
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Early Universe
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Brane Oscillations
• Seahra and Clarkson have calculated the GW emission in 5-D gravity when stellar mass black holes fall into a black hole
• Different from
the LF radiation from such
a system, there is also an
excitation of the
brane separation
itself
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This is a Source which exists!
But maybe in a universe which doesn’t
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Plasma-EMW instabilities
• Linearised field equations in terms of a small metric perturbation, h
• Interaction of EM Fields and EM Waves
42
2
22
2 161
c
Gh
tcx
FFFF
4
1
4
1
Increased charge density
contributes to stress energy
tensor
Tidal forces affect
chargedensity
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Nucleosynthesis limit
Cosmological Models
Current DetectorsCurrent Detectors
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Higher Energy Density
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Cosmological Models
Current DetectorsGalactic centre
Shadow Brane
Galactic CentreVisible Brane
Two element interferometer
Nucleosynthesis limit
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Statement
• The work presented here derives from many papers on EM-GW interactions published in properly peer reviewed journals since the 1970’s
• This work has no connection with (and does not support or endorse) ideas published by the HFGW group
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Conclusion
• Very high frequency gravitational waves may allow us to observe the very early universe, violent astrophysical events or exciting areas of new physics
• Current detectors are now beginning observations of the Galactic Centre at GHz and Optical Frequencies
• A two element interferometer is being designed jointly by Birmingham and Jodrell Bank
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Higher sensitivity
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Gravitational Waves in Space
• measure the separation between three spacecraft using laser beams.
• Use a long baseline so that the movement is larger.
• Measure separation to 10 pm 10-11 m over 5 million km.
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Other mechanisms
Bubble collisions Decay of Cosmic Strings
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“ Conversion” process• Inverse Gertsenshtein Effect
• EMW signal ~ h2L2K2B2
• Same frequency and direction as GW
• Must ensure phase coherence of EMW and GW
BEMW
L
h
Lens+CCD
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The Universe- and how we study it
• Everything we know about the Universe comes from studying electromagnetic waves ( Infra-red, X-rays, radio waves, etc) of different frequencies
• Different frequencies tell us about different temperature regimes
• But many of the problems in astrophysics are to do with mass, not temperature.
What can Gravity tell us?
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Measuring the waves:Interferometer
Laser
Photodiode
Mass
Mass
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The Largest Instrument Ever!
• Three spacecraft with laser beams between them in a solar orbit.
• The pattern rotates each year to scan the sky.
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How does a GW affect an EMW?
• Amplitude• Direction• Frequency• Polarisation state
quiescentsig hEE ~
GW
EMFieldhEnergySig2~
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lldp e
l
mm
MRkpcMxh 2/)5(
5.021 1.011
109
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Other Inflation Theories
• Garcia -Bellido
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What kind of Instrument?
• Interferometer sensitivity worsens as • Current best Upper Limit is by Akutsu,
Kawamura et al– 10-17 at 100 MHz
• So h ~ 10-23 at 1000Hz will be 10-20 at 1 GHz
221
min 14
8
1
P
ch
FLh
21
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