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## Basics of the Cosmic Microwave Background

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**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