Cosmic Microwave Background Polarization
and
Detection of Primordial Gravitational
Waves
Wen Zhao
@ Depart. of Astronomy, USTC
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OUTLINE
 CMB
field and Polarization
 Primordial
gravitational waves & CMB
 Conclusion
2
Temperature and Polarization of the CMB
3
E and B types of polarization of the CMB field
4
Thomson Scatter and
Generation of Polarization
Two factors:
** Temperature Anisotropies
** Free electrons
Two stages:
@ recombination stage
@ reionization stage
5
Perturbation Sources:
CMB power spectra
Density perturbation
Gravitational waves
r=1
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8
Polarization observations (Before BICEP2)
(Chiang et al 2010)
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Polarization observations (including BICEP2)
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Lensed B-mode
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Primordial gravitational
waves and CMB
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Generation of RGWs

In the curved space-time, the vacuum state at the stage 1 naturally
corresponds to the multi-particle state at a different stage 2.

If considering the Universe, we can assume the universe had a
vacuum state of graviton at the initial stage. With the expansion of the
Universe, but the radiation-dominant stage, the gravitons were
naturally generated. (Grishchuk, 1974)

If the Universe had an exact de-Sitter expansion in the inflationary
stage, the generated primordial power spectrum of RGWs is scaleinvariance. The amplitude of the spectrum directly depends on the
Hubble parameter, which directly relates to the energy scale of the
early Universe.
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Detecting in the CMB:
WMAP  Planck  (BICEP) CMBPOL
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CMB power spectra
Density perturbations
Relic gravitational waves
r=1
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Detection in the CMB

Method a: BB channel
But B-polarization is very small. When the noise is large, this
channel is useless.

Method b: TT+EE+TE channels
Total TT = TT (dp,+) + TT (gw,+)
Total EE = EE (dp,+) + EE (gw,+)
Total TE = TE (dp,+) + TE (gw,-)
This method is limited by cosmic variance of d.p. When r<0.05,
these three channels will be useless.
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Relic gravitational waves in WMAP data
WMAP7 gives: r<0.36 at 95% C.L. (Komatsu et al 2010)

This constraint comes from TT+TE observations.

(Planck)TT + (WMAP9)TE + highL even give: r<0.11 at 95% C.L. (Planck
Collaboration, 2013)

BB only gives r<2.1 at 95% C.L. (Komatsu et al 2010)
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Why?
 1. All
TT+TE data, the multipoles till to
around 10,000
 2.
Power-law form for d.p. is correct at least
for four orders in scale
WMAP low-multipole TE data
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WMAP TT+TE data (l<=100)

1. power-law forms for d.p. and g.w.

2. d.p. with running

5. piece-wise form for d.p. and g.w.

3. power-law d.p. and g.w., but
l<100 data (red curves)

4. power-law d.p. and g.w., but
l<100 data + SNIa + SDSS
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Using Planck (TT) + WMAP (TE) data
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Forecast for Planck: TT+EE+TE
Detecting B-mode Polarization by Planck

1. Planck can B-polarization, only if r>0.05.

2. Planck can only detect the reionization peak at l<10.

3. Planck is not good at for the detection of gravitational
waves (I will explain it later!).
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Planck mission and RGWs
------Simulated Planck data (r=0.1)
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Other Projects
S/N is determined by two factors:
1) sky survey area 2) noise level.
Planck: full sky but large noise
Ground: lower noise but small partial survey
CMBPOL or COrE: lower noise + full sky survey
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Planck or Ground-based experiment?
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Various ground-based experiments

Survey method: a small part of full sky for a long time.

Ground-based Experiments: QUaD, BICEP, QUIET, POLARBEAR,
ABS, CLASS, ClOVER, QUIJOTE, ACTPOL, SPTPOL, QUBIC,
KECK and so on.

Noise level: cosmic lensing limit.

In addition, balloon-borne experiments: EBEX, PIPER, Spider.
http://en.wikipedia.org/wiki/List_of_cosmic_microwave_background_experiments
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Current Observations (Before BICEP2)
(Chiang et al. 2010)
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BICEP1: Updated
(Barkast et al. 2014)
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BICEP2: Telescope in the mount
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BICEP2: Abstract
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BICEP2: Observed Q & U
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BICEP2: Constructed E & B
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BICEP2: BB Spectrum & RGWs
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Noise levels
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Detection limits
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Fourth Generation (Precise Measurement):
Planned CMBPOL experiment
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Testing inflationary consistency relation
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Ideal CMB experiment

Cosmic lensing generates the E-B
mixtures, and forms a nearly white Bmode spectrum.

For the ideal experiment, where only
the reduced cosmic lensing
contamination is considered.

Detection limit:
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Conclusion

CMB polarization was formed in the recombination stage (z~1100) and
reionization stage (z~10). Now, with the observing of Planck mission, as
well as other detectors, CMB polarization (including TE, EE and BB)
becomes one of the key probes of the early Universe.

Detection primordial gravitational waves, especially by the B-mode
polarization, is one of the main tasks for the current and future CMB
experiments, including Planck
, ground-based experiments
CMBPol
and ideal experiment
.

,
BICEP2 has detected the signal of gravitational waves with r=0.2, which
corresponds the energy scale of inflation
.
In principle, it can be confirmed by the forthcoming Planck polarization
data at different multipole range.
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THANKS!
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