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 (~1m
m)
A. Penzias & R. Wilson, 1965
R. Dicke and J. Peebles, 1965
3.5K
NOWP. 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
WMAP
COBE 1989
WMAP 2001
[COBE’s] measurements als o marked the inception of co smology as a precise science . It was not long before it was followed up, for instanc e by the WMAP satellite, whi ch yielded even clearer imag es of the background radiati on.
Press Release from th e Nobel Foundation
CMB: The Most Distant Light
CMB was emitted when the Universe was only 380,000 years ol d. 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 Spectrum
Scalar 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-lik e “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 Reionizati on
• 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 B ump”
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>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
