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Cosmic Microwave Background Polarization and Detection of Primordial Gravitational Waves. Wen Zhao @ Depart. of Astronomy, USTC. 1. OUTLINE. CMB field and Polarization Primordial gravitational waves & CMB Conclusion. 2. Temperature and Polarization of the CMB. 3.
@ Depart. of Astronomy, USTC
CMB field and Polarization
Primordial gravitational waves & CMB
Thomson Scatter and Generation of PolarizationTwo factors:** Temperature Anisotropies ** Free electronsTwo stages: @ recombination stage @ reionization stage
r = 1
(Chiang et al 2010)
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 scale-invariance. The amplitude of the spectrum directly depends on the Hubble parameter, which directly relates to the energy scale of the early Universe.
Relic gravitational waves
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.
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)
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
1. Planck can B-polarization, only if r>0.05.
2. Planck can only detect the reionization peak at l<10.
3. Planck is notgood at for the detection of gravitational waves (I will explain it later!).
S/N is determined by two factors:
1) sky survey area2) noise level.
Planck:full sky but large noise
Ground:lower noise but small partial survey
CMBPOL or COrE:lower noise + full sky survey
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.
(Chiang et al. 2010)
(Barkast et al. 2014)
Cosmic lensing generates the E-B mixtures, and forms a nearly white B-mode spectrum.
For the ideal experiment, where only the reduced cosmic lensing contamination is considered.
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.