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Searches for very high frequency gravitational waves Mike Cruise University of Birmingham 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 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 Very High Frequency detectors? • The best upper limit at 100 MHz by Akutsu and Kawamura of ~10-17 was with an interferometer 1 • But Interferometer sensitivity worsens as n 2 • 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 E or B Pathways for coupling EM and Gravity 2 1 n G n 2 2 h 16 4 T c t c 2 May contain EM Fields Fn g gn F Contain G potentials • 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 8GB L Spin states of g, B and n 3 c 2 2 What are the fluxes? • Flux of photons is times the flux of 2 c gravitons Flux 1 h 16G • EM Signal Power is P 1 8 0 2 2 B L K h cSin 2 2 2 2 2 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 Tidal forces affect charge density Increased charge density contributes to stress energy tensor • Linearised field equations in terms of a small metric 2 1 2 n 16G n perturbation, hn x 2 c 2 t 2 h c 4 • Interaction of EM Fields and EM Waves n 1 4 n 1 n F F F F 4 Current Detectors Nucleosynthesis limit Cosmological Models Higher Energy Density Current Detectors Galactic centre Shadow Brane Galactic Centre Visible Brane Two element interferometer Nucleosynthesis limit Cosmological Models 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 L Lens+CCD h B EMW • 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 Mass M a s s Laser Photodiode 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 Esig ~ hEquiescent 2 EnergySig ~ h EMField h 9 x10 21 1 1 0.1mm ( d 5l ) / 2l Mp e 0.5 Rkpc M l Other Inflation Theories • Garcia -Bellido What kind of Instrument? • Interferometer sensitivity worsens as hmin 1 4hc 8FL P 1 2 n 1 n 2 • 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 1 2