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 ~ was with an interferometer But Interferometer sensitivity worsens as Minimum detectable EM signal in a 1 Hz bandwidth ~ W Maximum EMW power ~ 10’s of MW ratio of min detectable signal ~ max available energy E or B

Pathways for coupling EM and Gravity 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 Spin 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

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 Increased charge density contributes to stress energy tensor Tidal forces affect charge density

Nucleosynthesis limit Cosmological Models Current Detectors

Higher Energy Density

Cosmological Models Current Detectors Galactic centre Shadow Brane Galactic Centre Visible 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 m over 5 million km.

Other mechanisms Bubble collisions Decay of Cosmic Strings

“ Conversion” process Inverse Gertsenshtein Effect EMW signal ~ h 2 L 2 K 2 B 2 Same frequency and direction as GW Must ensure phase coherence of EMW and GW B EMW 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 MassMass

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 GW

Other Inflation Theories Garcia -Bellido

What kind of Instrument? Interferometer sensitivity worsens as Current best Upper Limit is by Akutsu, Kawamura et al – at 100 MHz So h ~ at 1000Hz will be at 1 GHz