#### Transcript CERCA - LIGO

What can gravitational waves do to probe early cosmology? WMAP 2003 Barry C. Barish Caltech “Kavli-CERCA Conference on the Future of Cosmology” Case Western Reserve University October 10-12, 2003 LIGO-G030556-00-M 1 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 2 GW Stochastic Backgrounds Primordial stochastic backgrounds: relic GWs produced in the early Universe Cosmology Unique laboratory for fundamental physics at very high energy 3 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 4 The Gravitational Wave Signal The spectrum: The characteristic amplitude 5 What we know limits on primordial backgrounds The fluctuation of the temperature of the cosmic microwave background White dwarf and neutron radiation. A strong background of star binary system has gravitational atare very long ms waves pulsars fantastic second clock, the orbital wavelengths produces a stochastic clocks! Stability places period! Change in orbital redshift on the frequencies of 4the The primordial abundance of He limit on gravitational waves period can be computed in photons of the 2.7 K radiation, and is exponentially sensitive tothe thepulsar passing between GR, simplifying fitting. therefore aand fluctuation in This theirsets freeze-out temperature. us. Integrating for one Gives limit from 10-11temperature to limit on the number relic year givesof limit at f ~ 4.4 4.4 10-9 Hz gravitons. 10-9 Hz 6 - Theoretical Predictions Some theoretical “prediction” Strings Super-string Inflation Phase transition Maggiore 2000 7 Expected Signal Strength log Omega(f) Nucleosynthesis -5 ? -10 Slow-roll inflation -15 -6 -3 0 3 6 log f 8 Detection of Gravitational Waves Gravitational Wave Astrophysical Source Terrestrial detectors Detectors in space Virgo, LIGO, TAMA, GEO AIGO LISA 9 Astrophysics Sources frequency range Gravitational Waves can be studied over ~10 orders of magnitude in frequency terrestrial + space Audio band 10 Interferometer Concept Arms in LIGO are 4km Laser used to measure relative Measure difference in lengths of two length to one part in orthogonal arms 1021 or 10-18 meters …causing the interference pattern to change at the photodiode As a wave Suspended passes, the Masses arm lengths change in different ways…. 11 International Network Network Required for: » Detection Confidence » Waveform Extraction » Direction by Triangulation TAMA300 Tokyo LIGO Hanford, WA LIGO Livingston, LA GEO600 Hanover Germany VIRGO Pisa, Italy 12 + “Bar Detectors” : Italy, Switzerland, Louisiana, Australia Stochastic Background Signal auto-correlation 13 Overlap Reduction Function 14 Simultaneous Detection LIGO Hanford Observatory MIT Caltech Livingston Observatory 15 LIGO Livingston Observatory 16 LIGO Hanford Observatory 17 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 18 LIGO Sensitivity Livingston 4km Interferometer First Science Run 17 days - Sept 02 May 01 Jan 03 Second Science Run 59 days - April 03 19 Signals from the Early Universe Strength specified by ratio of energy density in GWs to total energy density needed to close the universe: ΩGW (f) 1 ρcritical dρGW d(lnf) Detect by cross-correlating output of two GW detectors: First LIGO Science Data Hanford - Livingston 20 Limits: Stochastic Search 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 Non-negligible LHO 4km-2km (H1-H2) instrumental crosscorrelation; currently being investigated. Previous best upper limits: » Garching-Glasgow interferometers : ΩGW (f) 3 10 5 » EXPLORER-NAUTILUS (cryogenic bars): ΩGW (907Hz) 60 21 Gravitational Waves from the Early Universe results projected E7 S1 S2 LIGO Adv LIGO 22 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. 23 LISA: Sources and Sensitivity 24 LISA: Astrophysical Backgrounds 25 Detecting the Anisotropy (1) Break-up the yrs long data set in short (say a few hrs long) chunks (2) Construct the new signal (3) Search for peaks in S(t): The LISA motion is periodic S m observable is the 26 Instrument’s sensitivity LIGO-I Advanced LIGO 3rd generation LISA Correlation of 2 LISA’s Slow-roll inflation 27 Sensitivity Primordial Stochastic Background 28 Stochastic Background Astrophysical 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 extragalactic) (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 (extragalactic) (Rajagopal and Romani, 1995) 29 Astrophysical Signals Limit Sensitivity for Primordial Sources Extragalactic WD-WD 10-10 Extragalactic NS-NS WD-WD LISA - 1yr 10-16 10-13 30 Ultimate GW Stochastic Probes log Omega(f) 3rd generation sensitivity limit (1yr) ? -11 WD-WD -12 NS-NS -13 CLEAN LISA sensitivity limit (1yr) -14 NS BH-MBH CORRUPTED -15 -16 -6 -5 -4 -3 -2 -1 0 1 2 3 log f 31 Future experiments in the “gap” (?) 10-18 MBH-MBH coalescences h Earth 90° LIGO 10-20 SN 90° Sun 10-22 NS LISA Unresolved Binaries 10-24 LISA II 10-26 10-7 A. Vecchio 10-5 10-3 10-1 101 103 Frequency [Hz] 32 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) 33