Cosmic Microwave Background Polarization and Detection of Primordial Gravitational Waves

1. Cosmic Microwave Background Polarization and Detection of Primordial Gravitational Waves Wen Zhao @ Depart. of Astronomy, USTC 1

2. OUTLINE CMB field and Polarization Primordial gravitational waves & CMB Conclusion 2

3. Temperature and Polarization of the CMB 3

4. E and B types of polarization of the CMB field 4

5. Thomson Scatter and Generation of PolarizationTwo factors:** Temperature Anisotropies ** Free electronsTwo stages: @ recombination stage @ reionization stage 5

6. Perturbation Sources:

7. CMB power spectra Density perturbation Gravitational waves r = 1 7

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9. Polarization observations (Before BICEP2) (Chiang et al 2010) 9

10. Polarization observations (including BICEP2) 10

11. Lensed B-mode 11

12. Primordial gravitational waves and CMB 12

13. 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 scale-invariance. The amplitude of the spectrum directly depends on the Hubble parameter, which directly relates to the energy scale of the early Universe. 13

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17. Detecting in the CMB: WMAP  Planck  (BICEP) CMBPOL 17

18. CMB power spectra Density perturbations Relic gravitational waves r=1 18

19. 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. 19

20. 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) 20

21. 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

22. WMAP low-multipole TE data 22

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24. 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 24

25. Using Planck (TT) + WMAP (TE) data 25

26. Forecast for Planck: TT+EE+TE

27. 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 notgood at for the detection of gravitational waves (I will explain it later!). 27

28. Planck mission and RGWs------Simulated Planck data (r=0.1) 28

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30. Other Projects 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 30

31. PlanckorGround-based experiment? 31

32. 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 32

33. Current Observations (Before BICEP2) (Chiang et al. 2010) 33

34. BICEP1: Updated (Barkast et al. 2014) 34

35. BICEP2: Telescope in the mount 35

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37. BICEP2: Abstract 37

38. BICEP2: Observed Q & U 38

39. BICEP2: Constructed E & B 39

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41. BICEP2: BB Spectrum & RGWs 41

42. Noise levels 42

43. Detection limits 43

44. Fourth Generation (Precise Measurement): Planned CMBPOL experiment 44

45. Testing inflationary consistency relation 45

46. Ideal CMB experiment 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. Detection limit: 46

47. 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. 47

48. THANKS! 48