Measurements of Cosmological Parameters

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Measurements of Cosmological Parameters

• Amedeo Balbi
• Dipartimento di Fisica INFN
• Università di Roma Tor Vergata

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Background Cosmology
Expanding universe, described by Friedmann
equation
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Perturbations Inflation
Inflation generates perturbations through
amplification of quantum fluctuations. In the
basic picture, they obey Gaussian statistics,
with a Harrison-Zeldovich power spectrum
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Parameters from the CMB
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CMB Anisotropy
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CMB Power Spectrum
Bennet et al. 2003
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Total Density
The typical angular size of fluctuations on the
CMB depends on the global geometry of the
Universe (? 1st peak position)
The universe is flat
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Hubble Constant

• HST Key Project use Cepheids to calibrate
  distance indicators (z0)
• Combining X-ray flux and SZ effect in clusters of
  galaxies (z0.5)
• CMB conformal distance to the decoupling surface
  (z1000)

Spergel et al. 2003
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Cosmic Ages
Spergel et al. 2003
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Baryon Abundance
CMB, ratio of acoustic peaks amplitude (Spergel
et al. 2003)
Primordial abundance of deuterium BBN (Fields
Sarkar, 2004)
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Primordial Abundances
Fields Sarkar, 2004
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Matter Density
Power spectrum from redshift surveys (e.g., 2dF,
SDSS)
Clusters of galaxies (e.g., Chandra)
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Something Missing!
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Type Ia Supernovae
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Cosmic Concordance
1 (CMB)
1/3 (LSS)
2/3 (SN)
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Amplitude of fluctuations
Spergel et al. 2003
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Inflation

• Universe is flat
• Primordial perturbations are adiabatic, Gaussian
  and scale-invariant (spectral index near unity)
• Gravitational wave background (tensor modes) is
  negligible

No viable alternative makes all these predictions
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Problems with Lambda
Vacuum fluctuations in QFT
Why now?
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Dark Energy?
Ideal fluid with generic equation of state
E.g., scalar field
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Constraints on Dark Energy
Seljak et al. 2004
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Precision Cosmology