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Cosmic Microwave Background Cosmic Microwave Background Polarization and Polarization and

Detection of Primordial Detection of Primordial

Gravitational WavesGravitational Waves

Wen ZhaoWen Zhao@ Depart. of Astronomy, USTC

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OUTLINE

CMB field and Polarization

Primordial gravitational waves & CMB

Conclusion

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Temperature and Polarization of the CMB

E and B types of polarization of the CMB field

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Thomson Scatter and Generation of Polarization

Two factors:** Temperature Anisotropies ** Free electrons

Two stages: @ recombination stage @ reionization stage

Perturbation Sources:

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CMB power spectra

r = 1

Density perturbation Gravitational waves

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Polarization observations (Before BICEP2)

(Chiang et al 2010)

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 scale-invariance. 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 WMAP Planck Planck (BICEP) (BICEP) CMBPOL CMBPOL

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CMB power spectraDensity 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 cha

nnel 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, th

ese 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)

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

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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

Forecast for Planck: TT+EE+TE

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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)

34(Barkast et al. 2014)

BICEP1: Updated

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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 B-mode 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 rei

onization 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!