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Measurements of Cosmological Parameters

This presentation delves into the fundamental concepts of cosmology, focusing on the expanding universe described by the Friedmann equation. It examines gravitational perturbations generated during inflation and their implications for cosmic microwave background (CMB) anisotropy and power spectra. Key topics include the universe's geometry, Hubble constant determinations, baryon abundance, and variations in matter density as determined by large-scale surveys. The discussion emphasizes precision cosmology, the significance of primordial perturbations, and the intriguing challenges posed by dark energy.

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Measurements of Cosmological Parameters

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  1. Measurements of Cosmological Parameters Amedeo Balbi Dipartimento di Fisica & INFN Università di Roma “Tor Vergata”

  2. Background Cosmology Expanding universe, described by Friedmann equation:

  3. 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:

  4. Parameters from the CMB

  5. CMB Anisotropy

  6. CMB Power Spectrum Bennet et al. 2003

  7. 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

  8. 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

  9. Cosmic Ages Spergel et al. 2003

  10. Baryon Abundance CMB, ratio of acoustic peaks amplitude (Spergel et al. 2003): Primordial abundance of deuterium + BBN (Fields & Sarkar, 2004):

  11. Primordial Abundances Fields & Sarkar, 2004

  12. Matter Density Power spectrum from redshift surveys (e.g., 2dF, SDSS): Clusters of galaxies (e.g., Chandra):

  13. Something Missing!

  14. Type Ia Supernovae

  15. Cosmic Concordance 1 (CMB) 1/3 (LSS) 2/3 (SN)

  16. Amplitude of fluctuations Spergel et al. 2003

  17. 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

  18. Problems with Lambda Vacuum fluctuations in QFT: “Why now?”:

  19. Dark Energy? Ideal fluid with generic equation of state: E.g., scalar field:

  20. Constraints on Dark Energy Seljak et al. 2004

  21. Precision Cosmology

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