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Measurements of Cosmological Parameters. Amedeo Balbi Dipartimento di Fisica & INFN Università di Roma “Tor Vergata”. Background Cosmology. Expanding universe, described by Friedmann equation:. Perturbations & Inflation.
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Measurements of Cosmological Parameters Amedeo Balbi Dipartimento di Fisica & INFN Università di Roma “Tor Vergata”
Background Cosmology Expanding universe, described by Friedmann equation:
Perturbations & Inflation Inflation generates perturbations through amplification of quantum fluctuations. In the basic picture, they obey Gaussian statistics, with a Harrison-Zel’dovich power spectrum:
CMB Power Spectrum Bennet et al. 2003
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
Hubble Constant • HST Key Project: use Cepheids to calibrate distance indicators (z~0) • Combining X-ray flux and SZ effect in clusters of galaxies (z~0.5) • CMB: conformal distance to the decoupling surface (z~1000) Spergel et al. 2003
Cosmic Ages Spergel et al. 2003
Baryon Abundance CMB, ratio of acoustic peaks amplitude (Spergel et al. 2003): Primordial abundance of deuterium + BBN (Fields & Sarkar, 2004):
Primordial Abundances Fields & Sarkar, 2004
Matter Density Power spectrum from redshift surveys (e.g., 2dF, SDSS): Clusters of galaxies (e.g., Chandra):
Cosmic Concordance 1 (CMB) 1/3 (LSS) 2/3 (SN)
Amplitude of fluctuations Spergel et al. 2003
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
Problems with Lambda Vacuum fluctuations in QFT: “Why now?”:
Dark Energy? Ideal fluid with generic equation of state: E.g., scalar field:
Constraints on Dark Energy Seljak et al. 2004