Basics of the Cosmic Microwave Background Eiichiro Komatsu (UT Austin) Lecture at Max Planck Institute August 14, 2007
3.5K NOW R. Dicke and J. Peebles, 1965
P. Roll and D. Wilkinson, 1966 D.Wilkinson “The Father of CMB Experiment”
David Wilkinson (1935~2002) • Science Team Meeting, July, 2002 • Plotted the “second point” (3.2cm) on the CMB spectrum • The first confirmation of a black-body spectrum (1966) • Made COBE and MAP happen and be successful • “The Father of CMB Experiment” • MAP has become WMAP in 2003
COBE/DMR, 1992 • Isotropic? • CMB is anisotropic! (at the 1/100,000 level)
COBE to WMAP COBE 1989 COBE Press Release from the Nobel Foundation [COBE’s] measurements also marked the inception of cosmology as a precise science. It was not long before it was followed up, for instance by the WMAP satellite, which yielded even clearer images of the background radiation. WMAP WMAP 2001
CMB: The Most Distant Light CMB was emitted when the Universe was only380,000 years old. WMAP has measured the distance to this epoch. From (time)=(distance)/c we obtained13.73 0.16 billion years.
What Temperature Tells Us Distance to z~1100 Baryon-to-Photon Ratio Dark Energy/ New Physics? Matter-Radiation Equality Epoch
CMB to Cosmology Low Multipoles (ISW) &Third Baryon/Photon Density Ratio Constraints on Inflation Models
Power Spectrum Scalar T Tensor T Scalar E Tensor E Tensor B
Seljak & Zaldarriaga (1997); Kamionkowski, Kosowsky, Stebbins (1997) Jargon: E-mode and B-mode • Polarization is a rank-2 tensor field. • One can decompose it into a divergence-like “E-mode” and a vorticity-like “B-mode”. E-mode B-mode
Primordial Gravity Waves • Gravity waves create quadrupolar temperature anisotropy -> Polarization • Directly generate polarization without kV. • Most importantly, GW creates B mode.
Polarization From Reionization • CMB was emitted at z~1088. • Some fraction of CMB was re-scattered in a reionized universe. • The reionization redshift of ~11 would correspond to 365 million years after the Big-Bang. IONIZED z=1088, t～1 NEUTRAL First-star formation z～11, t～0.1 REIONIZED z=0
Measuring Optical Depth • Since polarization is generated by scattering, the amplitude is given by the number of scattering, or optical depth of Thomson scattering: which is related to the electron column number density as
Polarization from Reioniazation “Reionization Bump”
Parameter Determination: First Year vs Three Years • The simplest LCDM model fits the data very well. • A power-law primordial power spectrum • Three relativistic neutrino species • Flat universe with cosmological constant • The maximum likelihood values very consistent • Matter density and sigma8 went down slightly
Constraints on GW • Our ability to constrain the amplitude of gravity waves is still coming mostly from the temperature spectrum. • r<0.55 (95%) • The B-mode spectrum adds very little. • WMAP would have to integrate for at least 15 years to detect the B-mode spectrum from inflation.
What Should WMAP Say About Inflation Models? Hint for ns<1 Zero GW The 1-d marginalized constraint from WMAP alone is ns=0.95+-0.02. GW>0 The 2-d joint constraint still allows for ns=1 (HZ).
What Should WMAP Say About Flatness? Flatness, or very low Hubble’s constant? If H=30km/s/Mpc, a closed universe with Omega=1.3 w/o cosmological constant still fits the WMAP data.
What Should WMAP Say About Dark Energy? Not much! The CMB data alone cannot constrain w very well. Combining the large-scale structure data or supernova data breaks degeneracy between w and matter density.
What Should WMAP Say About Neutrino Mass? WMAP alone (95%): - Total mass < 2eV WMAP+SDSS (95%) - Total mass < 0.9eV WMAP+all (95%) - Total mass < 0.7eV