Testing the slow roll inflation paradigm with the Big Bang Observer

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Testing the slow roll inflation paradigmwith the
Big Bang Observer

• Carlo Ungarelli
• School of Physics and Astronomy
• Astrophysics and Space Research Group
• In collaboration with A.Vecchio, P. Corasaniti
  (Columbia, NY), R. A. Mercer

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• The paradigm of (slow-roll) inflation
• Solves the shortcomings of the standard
  cosmological model (flatness and horizon problem)
  by postulating the existence of an early phase of
  accelerated expansion driven by the energy
  density of a scalar field slowly rolling towards
  its minimum
• Predictions 1)The Universe is spatially flat
  2)Quantum zero-point fluctuations of space-time
  metric are stretched over astrophysical scales
  producing a nearly scale invariant spectrum of
  density perturbations and a spectrum of
  gravitational waves as a cosmic gravitational
  wave stochastic background (CGWB)
• The first prediction and part of the second have
  been confirmed by the measurement of the Cosmic
  Microwave Background (CMB). The existence of CGWB
  is yet untested

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CGWB produced during slow-roll inflation
COBE bound (Koranda, Turner 94)
Almost flat spectrum (see e.g. Turner 97)
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Detection of stochastic backgrounds
Earth-based interferometers Design sensitivity
of current Interferometers Second generation
detectors Advanced LIGO 3rd generation
European Gravitational Observatory

• String-inspired inflationary models
• (e.g. pre-big-bang) could be tested by second
  generation detectors
• (Allen, Brustein 97 U, Vecchio 99)
• Warnings the models do not provide
• reliable description of transition to
• Post-big-bang era the observability of GW
  spectrum depends on the detail of the transition

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Detection of stochastic background LISA
Astrophysical backgrounds Incoherent
superposition of GW emitted by short-period,
solar mass binary systems (WD,NS..) Galactic and
extra-galactic contribution (Bender et al,
90,97 Postnov et al, Schneider et al 00)
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Towards testing slow-roll inflation BBO
To avoid the astrophysical background the
frequency band should be around 0.1 Hz (U and
Vecchio 01, Bender and Hogan 01, Seto et al 01)
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GWs in single field slow-roll inflation
Curvature (R) and Tensor (T) perturbations
spectra
(See Turner 97)
The GW spectrum depends on two primordial
parameters (r,nS) and one cosmological parameter
A (0.7 see e.g. Spergel et al 03)
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BBO-lite
BBO
(U, Vecchio,Corasaniti, Mercer Astro-ph/to
appear)
BBO-grand
WMAP 1,2,3-s confidence levels (Kinney et al 04)
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BBO vs future CMB experiments (I)
BBO vs PLANCK
BBO-GRAND vs CMBPol
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BBO vs future CMB experiments (II)
CMB B-mode Foregrounds from gravitational
lensing impose a lower limit (Knox and Song
02)
Residual foregrounds from NS-radio pulsars
BBO design sensitivity depends strongly on the
antenna diameter and laser wavelength
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Some Remarks

• Advanced earth-based GW detectors cannot test the
  standard slow-roll inflation paradigm. They could
  detect signal from inflation if Universe
  underwent a pre-big-bang phase (or
  accelerated contraction). More robust predictions
  are needed.
• A dedicated post-LISA mission can detect a
  stochastic background of GW produced during an
  epoch of slow-roll inflation with a design
  sensitivity beyond the sensitivity of PLANCK
  surveyor one. The sensitivity of post-PLANCK
  missions to stochastic backgrounds of GW
  strongly depends on the ability of removing the
  foregrounds due to lensing