Basics of the Cosmic Microwave Background

Eiichiro Komatsu (UT Austin)

Lecture at Max Planck Institute

August 14, 2007

Night Sky in Optical (~0.5nm)

Night Sky in Microwave (~1mm)

A. Penzias & R. Wilson, 1965

R. Dicke and J. Peebles, 1965

3.5KNOW

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 WMAPCOBE

WMAP

COBE1989

WMAP2001

[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.

Press Release from the Nobel Foundation

CMB: The Most Distant Light

CMB was emitted when the Universe was only 380,000 years old. WMAP has measured the distance to this epoch. From (time)=(distance)/c we obtained 13.73 0.16 billion years.

WMAP 3-yr Power Spectrum

What Temperature Tells Us

Distance to z~1100

Baryon-to-Photon Ratio

Matter-Radiation Equality Epoch

Dark Energy/New Physics?

CMB to Cosmology

&Third

Baryon/Photon Density Ratio

Low Multipoles (ISW)

Constraints on Inflation Models

Determining Baryon Density

Determining Dark Matter Density

Measuring Geometry

Power SpectrumScalar T

Tensor T

Scalar E

Tensor E

Tensor B

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

Seljak & Zaldarriaga (1997); Kamionkowski, Kosowsky, Stebbins (1997)

Primordial Gravity Waves• Gravity waves create quadrupolar temperat

ure 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 3

65 million years after the Big-Bang.

z=1088, ～ 1

z～ 11, ～0.1

First-star formation

z=0

IONIZED

REIONIZED

NEUTRAL

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”

WMAP Results

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>0The 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