Measurements of Cosmological Parameters
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Transcript of Measurements of Cosmological Parameters
Measurements of Cosmological ParametersAmedeo BalbiDipartimento di Fisica & INFNUniversità di Roma “Tor Vergata”
Background CosmologyExpanding universe, described by Friedmann equation:
20
2
2 3
1 Maa a a
H
-1 -10 100 km s Mpc
M
M B DM
h H
Perturbations & InflationInflation generates perturbations through amplification of quantum fluctuations. In the basic picture, they obey Gaussian statistics, with a Harrison-Zel’dovich power spectrum:
( ) nP k Ak
Parameters from the CMB
CMB Anisotropy
CMB Power Spectrum
Bennet et al. 2003
Total DensityThe typical angular size of fluctuations on the CMB depends on the global geometry of the Universe ( 1st peak position)
1.02 0.02
The universe is flat
Hubble ConstantHST 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 AbundanceCMB, ratio of acoustic peaks amplitude (Spergel et al. 2003):
Primordial abundance of deuterium + BBN (Fields & Sarkar, 2004):
2 0.024 0.001Bh
20.012 0.025 (95% CL)Bh
Primordial Abundances
Fields & Sarkar, 2004
Matter DensityPower spectrum from redshift surveys (e.g., 2dF, SDSS):
0.6
0.18 0.020.17 0.06
0.49 0.09( 1)
M
B M
M
h
bb
Clusters of galaxies (e.g., Chandra):
0.3BB M
M
f
Something Missing!
1 0.3M
Type Ia Supernovae
20 0
1 12LH d z q z
00 2
0
02Maq
a
0.7
Cosmic Concordance
M 1
(CMB)1/3
(LSS)2/3(SN)
Amplitude of fluctuations
Spergel et al. 2003
InflationUniverse is flatPrimordial 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 LambdaVacuum fluctuations in QFT:
40 12010 10 “Why now?”:
3 when 1Ma a
Dark Energy?Ideal fluid with generic equation of state:
( )1 3
w a pw
E.g., scalar field:2
2
2 ( )
2 ( )
V
p V
Constraints on Dark Energy
Seljak et al. 2004
Precision Cosmology