Searches for very high frequency gravitational waves

1. Searches for very high frequency gravitational waves Mike Cruise University of Birmingham

2. Signals from Neutron Stars

3. Signals from SMBH’s LIGO , Virgo, LISA or pulsar timing are most likely to make the first detections

4. Why go to higher frequencies? • Other branches of astronomy developed through mullti-frequency observations • For frequencies n>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

5. E or B 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

6. May contain EM Fields Contain G potentials Pathways for coupling EM and Gravity

7. How does a GW interact with a static EM Field? • De Logi and Mickelson (1977) Photon Graviton Virtual Photon ( Static Magnetic Field ) For one incoming graviton per second Spin states of g, B and n

8. What are the fluxes? • Flux of photons is G times the flux of gravitons • EM Signal Power is

10. Early Universe

11. 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

13. This is a Source which exists! But maybe in a universe which doesn’t

14. Plasma-EMW instabilities Increased charge density contributes to stress energy tensor Tidal forces affect charge density • Linearised field equations in terms of a small metric perturbation, hmn • Interaction of EM Fields and EM Waves

15. Current Detectors Current Detectors Nucleosynthesis limit Cosmological Models

18. Higher Energy Density

21. Current Detectors Two element interferometer Nucleosynthesis limit Galactic centre Shadow Brane Galactic Centre Visible Brane Cosmological Models

22. 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

23. 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

25. Higher sensitivity

26. 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.

27. Other mechanisms Bubble collisions Decay of Cosmic Strings

28. EMW B “ Conversion” process • Inverse Gertsenshtein Effect • EMW signal ~ h2L2K2B2 • Same frequency and direction as GW • Must ensure phase coherence of EMW and GW L Lens+CCD h

29. 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?

30. Measuring the waves:Interferometer Mass M a s s Laser Photodiode

31. The Largest Instrument Ever! • Three spacecraft with laser beams between them in a solar orbit. • The pattern rotates each year to scan the sky.

32. How does a GW affect an EMW? • Amplitude • Direction • Frequency • Polarisation state GW

34. Other Inflation Theories • Garcia -Bellido

35. 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