1. Gravitational Wave Detectors Course in Inflation, Structure formation and CMB 7 November 2002 Silvio Orsi

2. GW: My presentation • GW production • Upper bounds on GW background • Frequency range • Detectors for GW: • Under construction & future detectors • Frequency range & sensitivity • Noise • Examples

3. GW Production • GW background from amplification of vacuum fluctuations • Standard inflation • Pre-Big Bang cosmology • Other models • Known astrophysical sources • Noise (unresolved astrophysical sources) • On Earth: Seismic noise

4. GW Background • Origin • Characteristics: isotropic, stationary, unpolarized • Main property: frequency spectrum • 3 useful characterizations: • Energy density: • Spectral density • Characteristic amplitude

5. GW Background (ex.) http://www.ba.infn.it/~gasperin/

6. Upper bounds on Energy Density

7. GW Detectors • Existing detectors give upper bounds • Resonant mass experiments: EXPLORER (CERN), NAUTILUS (I), AURIGA (I), ALLEGRO (Louisiana), NIOBE (Aus) • Interferometers • Large-scale (under construction): LIGO, VIRGO (I,F), GEO600 (D), TAMA300 (Jap), AIGO (Aus) • Second generation (planned): LISA (space interf.), Advanced LIGO • Two-interferometer correlation • (Pulsars)

8. Resonant mass experiments • Bars are narrow-band detectors and work at two resonances • f ~ 1kHz • Half-heigth bandwiths ~ 1Hz • Strain sensitivity ~ 5x interferometers • Optimization = (Quality factor x Mass)/Temperature • AURIGA

9. AURIGA • Ultracryogenic Resonant Antenna for the Gravitational Astronomical Investigation • Resonant acoustic detector • Resonator: Aluminium bar (length=3m, diameter=60cm, mass=2.3t, T~100mK, Teff~mK, quality factor Q=106) • Signals @ ~1kHz

10. AURIGA

11. Interferometer: principles • Wide-band detectors (few Hz  kHz) • Description (see fig.) • Sensitivity • Noise (seismic, resonances, laser shot)

12. Typical sensitivity curve RESONANCE REGION

13. Two-interferometer correlation • Dramatic increase in sensitivity • Interf-interf • Interf-res. mass • Not applicable to LISA 5x10-11 Advanced LIGO

14. VIRGO • Pisa (Italy) • Arm length: 3km • Large collaboration: 11 laboratories (I,F) ~200 people • Sensitivity: http://www.virgo.infn.it

15. VIRGO http://wwwlapp.in2p3.fr/virgo/gwf.html

16. VIRGO Sensitivity

17. LIGO Laser Interferometer Gravitational Wave Observatory • Will evolve into LIGOIII with a sensibility 10x better than LIGOI

18. LISA Laser Interferometer Space Antenna • Proposed by ESA (1993) • NASA/ESA collaboration • Launch estimated 2010-2020 • Mission: 2yrs (up to 10) • 3 arms (redundancy) • Common noise (3 non-indep. interf.) • NSR (noise to signal ratio) negligible • Info on GW polarization & direction

19. LISA (2) Laser Interferometer Space Antenna • Better discrimination of GW stochastic bg, binaries, cosmological effects & instrumental noise • No seismic & gravity-gradient noise • Frequency range: 10-4 Hz  1 Hz • Very long length (L~5x106 km) • Strain sensitivity@1mHz ~ 4x10-21 Hz –1/2

20. LISA (3) Laser Interferometer Space Antenna • Frequency range: 10-4 Hz  1 Hz • Best sensitivity: 330 mHz • f>30mHz: GW<2L • f<3mHz: spurious forces on test masses • Low f: expected bg from white-dwarfs binaries

21. LISA (sensitivity) Laser Interferometer Space Antenna