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WMAP 2003

What can gravitational waves do to probe early cosmology? Barry C. Barish Caltech “Kavli-CERCA Conference on the Future of Cosmology” Case Western Reserve University October 10-12, 2003. WMAP 2003. LIGO-G030556-00-M. Signals from the Early Universe.

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WMAP 2003

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  1. What can gravitational waves do to probe early cosmology?Barry C. BarishCaltech“Kavli-CERCA Conference on the Future of Cosmology”Case Western Reserve University October 10-12, 2003 WMAP 2003 LIGO-G030556-00-M

  2. Signals from the Early Universe The smaller the cross-section, the earlier the particle decouples • Photons: T = 0.2 eV t = 300,000 yrs • Neutrinos: T = 1 MeV t ~ 1 sec • Gravitons: T = 1019 GeV t ~ 10-43 sec Cosmic Microwave background WMAP 2003

  3. GW Stochastic Backgrounds Primordial stochastic backgrounds:relic GWs produced in the early Universe • Cosmology • Unique laboratory for fundamental physics at very high energy

  4. GW Stochastic Backgrounds Astrophysically generated stochastic backgrounds (foregrounds):incoherent superposition of GWs from large populations of astrophysical sources • Populations of compact object in our galaxy and at high redshift • 3D distribution of sources • Star formation history

  5. The Gravitational Wave Signal • The spectrum: • The characteristic amplitude

  6. What we knowlimits on primordial backgrounds The fluctuation of the temperature of the cosmic microwave background radiation. A strong background of gravitational waves at very long wavelengths produces a stochastic redshift on the frequencies of the photons of the 2.7 K radiation, and therefore a fluctuation in their temperature White dwarf and neutron star binary system has second clock, the orbital period! Change in orbital period can be computed in GR, simplifying fitting. Gives limit from 10-11 to 4.4 10-9 Hz ms pulsars are fantastic clocks! Stability places limit on gravitational waves passing between the pulsar and us. Integrating for one year gives limit at f ~ 4.4 10-9 Hz The primordial abundance of 4He is exponentially sensitive to the freeze-out temperature. This sets limit on the number of relic gravitons. -

  7. Some theoretical “prediction” Theoretical Predictions Strings Super-string Inflation Phase transition Maggiore 2000

  8. Expected Signal Strength log Omega(f) -5 -10 -15 Nucleosynthesis ? Slow-roll inflation -6 -3 0 3 6 log f

  9. Detectionof Gravitational Waves Gravitational Wave Astrophysical Source Terrestrial detectors Virgo, LIGO, TAMA, GEO AIGO Detectors in space LISA

  10. Astrophysics Sourcesfrequency range Audio band • Gravitational Waves can be studied over ~10 orders of magnitude in frequency • terrestrial + space

  11. As a wave passes, the arm lengths change in different ways…. Interferometer Concept • Arms in LIGO are 4km • Measure difference in length to one part in 1021 or 10-18 meters • Laser used to measure relative lengths of two orthogonal arms …causing the interference pattern to change at the photodiode Suspended Masses

  12. International Network • Network Required for: • Detection Confidence • Waveform Extraction • Direction by Triangulation TAMA300 Tokyo LIGO Hanford, WA GEO600 Hanover Germany VIRGO Pisa, Italy LIGO Livingston, LA + “Bar Detectors” : Italy, Switzerland, Louisiana, Australia

  13. Stochastic Background Signal auto-correlation

  14. Overlap Reduction Function

  15. Simultaneous DetectionLIGO Hanford Observatory MIT Caltech Livingston Observatory

  16. LIGO Livingston Observatory

  17. LIGO Hanford Observatory

  18. What Limits LIGO Sensitivity? • Seismic noise limits low frequencies • Thermal Noise limits middle frequencies • Quantum nature of light (Shot Noise) limits high frequencies • Technical issues - alignment, electronics, acoustics, etc limit us before we reach these design goals

  19. LIGO Sensitivity Livingston 4km Interferometer May 01 First Science Run 17 days - Sept 02 Jan 03 Second Science Run 59 days - April 03

  20. Signals from the Early Universe • Strength specified by ratio of energy density in GWs to total energy density needed to close the universe: • Detect by cross-correlating output of two GW detectors: First LIGO Science Data Hanford - Livingston

  21. Interferometer Pair 90% CL Upper Limit Tobs LHO 4km-LLO 4km WGW (40Hz - 314 Hz) < 72.4 62.3 hrs LHO 2km-LLO 4km WGW (40Hz - 314 Hz) < 23 61.0 hrs Limits: Stochastic Search • Non-negligible LHO 4km-2km (H1-H2) instrumental cross-correlation; currently being investigated. • Previous best upper limits: • Garching-Glasgow interferometers : • EXPLORER-NAUTILUS (cryogenic bars):

  22. Gravitational Waves from the Early Universe E7 results projected S1 S2 LIGO Adv LIGO

  23. Interferometers in Space The Laser Interferometer Space Antenna (LISA) • The center of the triangle formation will be in the ecliptic plane • 1 AU from the Sun and 20 degrees behind the Earth.

  24. LISA: Sources and Sensitivity

  25. LISA: Astrophysical Backgrounds

  26. Detecting the Anisotropy (1) Break-up the yrs long data set in short (say a few hrs long) chunks (2) Construct the new signal The LISA motion is periodic (3) Search for peaks in S(t): is the observable

  27. Instrument’s sensitivity LIGO-I Advanced LIGO 3rd generation LISA Correlation of 2 LISA’s Slow-roll inflation

  28. Sensitivity Primordial Stochastic Background

  29. Stochastic BackgroundAstrophysical Foregrounds • White-dwarf binary systems(galactic and extra-galactic) (Hils et al, 1990; Schneider et al, 2001) • Neutron star binary systems(galactic and extra-galactic) (Schneider et al, 2001) • Rotating neutron stars(galactic and extra-galactic) (Giazzotto et al, 1997; Regimbau and de Freitas Pacheco, 2002) • Solar mass compact objects orbiting a massive black hole(extra-galactic) (Phinney 2002) • Super-massive black hole binaries(extra-galactic) (Rajagopal and Romani, 1995)

  30. Astrophysical SignalsLimit Sensitivity for Primordial Sources Extra-galactic WD-WD 10-10 WD-WD Extra-galactic NS-NS LISA - 1yr 10-16 10-13

  31. Ultimate GW Stochastic Probes log Omega(f) -11 -12 -13 -14 -15 -16 3rd generation sensitivity limit (1yr) ? WD-WD NS-NS CLEAN LISA sensitivity limit (1yr) NS BH-MBH CORRUPTED -6 -5 -4 -3 -2 -1 0 1 2 3 log f

  32. 10-18 MBH-MBH coalescences h LIGO 10-20 SN NS 10-22 LISA Unresolved Binaries 10-24 LISA II 50 000 km 10-26 Earth 90° 60° 103 10-7 10-3 101 10-5 10-1 Sun 90° Frequency [Hz] Future experiments in the “gap” (?) A. Vecchio

  33. Conclusions • Primordial Gravitational Wave Stochastic Background is potentially a powerful probe of early cosmology • Present/planned earth/space-based interferometers will begin to probe the sensitivity regime of interest. • They will either set limits constraining early cosmology or detect the stochastic background • They are ultimately limited to ~10-11 and 10-13 in energy density • A future short arm space probe could probe the gap(0.1 – 1 Hz region looks cleanest)

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