The Polarization of the CMB

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The Polarization of the CMB
DASI
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Overview

• Physical origin of polarization
• The information encoded by polarization
• Summary

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The Anisotropies are polarized
DASI
Kovac et al. astro-ph/0209478
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The polarization and temperature patterns are
correlated.
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How is polarization generated?
Thomson Scattering
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Recombination
T 0.3 eV ltlt me c2
Hydrogen is neutral
Hydrogen is ionized Thomson Scattering
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The quadrupole created by density perturbations
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Polarization peaks at smaller scales
Peaks are out of phase
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The quadrupole created by GW
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Anisotropies created by GW
ISW like effect, produced after recombination
Polarization is produced at recombination
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What can we learn ?

• B Modes pattern of vectors
• After recombination Reionization Bump,
  lensing
• At recombination Acoustic peaks

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Information in polarization

• Improvement in parameter constraints
  consistency checks
• Test super-horizon nature of perturbations
• Features in the primordial power spectrum
• Isocurvature components
• Test of time evolution of physical constants
• Constrain how and when the universe reionized
• Measure mass distribution along the line of
  sight (lensing)
• Detect gravity waves from inflation

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The Information in the patternE-B Decomposition
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Density pert. Gravity Waves
Gravity Waves
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Power spectra of E B
E modes
B modes
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Gravity waves from Inflation
Each polarization of the GW fluctuates during
inflation by (
)
Directly measure the expansion rate during
Inflation
(limit imposed by lensing)
If
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Super-horizon perturbations
Observer
2o
Decoupling
Initial conditions
Spergel MZ
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The sign of the TE cross correlation
Causal seed model
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After Recombination
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Gravitational Lensing
Lensing induced B modes
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• The height of the bump is given by the optical
  depth
• The quadrupole is produced by the free streaming
  of the monopole at recombination, k 2/(?reio
  -?rec) produces the biggest quadrupole
• Angular scale l (?o - ?reio )/(?reio -?rec)

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WMAP Spectra
Negative bump super-horizon perturbations
Large scale polarization Optical depth 0.1
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Summary

• The CMB is slightly polarized
• Polarization is generated by Thomson scattering
  of radiation that had a quadrupole anisotropy
• For density modes, polarization is roughly
  proportional to the velocity gradient across the
  mean free path
• A stochastic background of gravitational waves
  leave a characteristic signature
• GW produced in inflation are observable if E
  1016 GeV
• Reionization leaves an signature on large scales
• Secondary effects such a lensing can create B
  even if there are no GW