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

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Night Sky in Optical (0.5nm)
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Night Sky in Microwave (1mm)
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A. Penzias R. Wilson, 1965
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R. Dicke and J. Peebles, 1965
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P. Roll and D. Wilkinson, 1966
D.Wilkinson The Father of CMB Experiment
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David Wilkinson (19352002)

• 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
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COBE/DMR, 1992

• Isotropic?
• CMB is anisotropic! (at the 1/100,000 level)

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COBE to WMAP
COBE 1989
COBE
Press Release from the Nobel Foundation
COBEs 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
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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.
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WMAP 3-yr Power Spectrum
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What Temperature Tells Us
Distance to z1100
Baryon-to-Photon Ratio
Dark Energy/ New Physics?
Matter-Radiation Equality Epoch
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CMB to Cosmology
Low Multipoles (ISW)
Third
Baryon/Photon Density Ratio
Constraints on Inflation Models
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Determining Baryon Density
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Determining Dark Matter Density
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Measuring Geometry
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Power Spectrum
Scalar T

• Tensor T

Scalar E
Tensor E
Tensor B
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Jargon E-mode and B-mode
Seljak Zaldarriaga (1997) Kamionkowski,
Kosowsky, Stebbins (1997)

• 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
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Primordial Gravity Waves

• Gravity waves create quadrupolar temperature
  anisotropy -gt Polarization
• Directly generate polarization without kV.
• Most importantly, GW creates B mode.

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Polarization From Reionization

• CMB was emitted at z1088.
• 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
z1088, t1
NEUTRAL
First-star formation
z11, t0.1
REIONIZED
z0
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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

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Polarization from Reioniazation

• Reionization Bump

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WMAP Results
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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

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Constraints on GW

• Our ability to constrain the amplitude of gravity
  waves is still coming mostly from the temperature
  spectrum.
• rlt0.55 (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.

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What Should WMAP Say About Inflation Models?
Hint for nslt1 Zero GW The 1-d marginalized
constraint from WMAP alone is ns0.95-0.02.
GWgt0 The 2-d joint constraint still allows for
ns1 (HZ).
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What Should WMAP Say About Flatness?
Flatness, or very low Hubbles constant? If
H30km/s/Mpc, a closed universe with Omega1.3
w/o cosmological constant still fits the WMAP
data.
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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.
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What Should WMAP Say About Neutrino Mass?
WMAP alone (95) - Total mass lt 2eV WMAPSDSS
(95) - Total mass lt 0.9eV WMAPall (95) -
Total mass lt 0.7eV