Searches for very high frequency gravitational waves

Mike Cruise

University of Birmingham

Searches for very high frequency gravitational waves

Signals from Neutron Stars

Signals from SMBH’s

LIGO , Virgo, LISA or pulsar timing are most likely to make the first detections

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

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

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

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

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

Early Universe

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

This is a Source which exists!

But maybe in a universe which doesn’t

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

Nucleosynthesis limit

Cosmological Models

Current DetectorsCurrent Detectors

Higher Energy Density

Cosmological Models

Current DetectorsGalactic centre

Shadow Brane

Galactic CentreVisible Brane

Two element interferometer

Nucleosynthesis limit

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

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

Higher sensitivity

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.

Other mechanisms

Bubble collisions Decay of Cosmic Strings

“ 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

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?

Measuring the waves:Interferometer

Laser

Photodiode

Mass

Mass

The Largest Instrument Ever!

• Three spacecraft with laser beams between them in a solar orbit.

• The pattern rotates each year to scan the sky.

How does a GW affect an EMW?

• Amplitude• Direction• Frequency• Polarisation state

quiescentsig hEE ~

GW

EMFieldhEnergySig2~

lldp e

l

mm

MRkpcMxh 2/)5(

5.021 1.011

109

Other Inflation Theories

• Garcia -Bellido

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