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Determination of tensor spectral index in the CMB. Wen Zhao @ IHEP . 2012. Introduction. The models of inflation predict the primordial power spectrum of the primordial (relic) gravitational waves. Detection of RGWs provides a chance to study how the Universe was born. - PowerPoint PPT Presentation
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Determination of tensor spectral index in the CMB
Wen Zhao @ IHEP . 2012
Introduction• The models of inflation predict the primordial power spect
rum of the primordial (relic) gravitational waves.
• Detection of RGWs provides a chance to study how the Universe was born.
• The only way to detect very low frequency RGWs is by studying the Cosmic Microwave Background Radiation (CMB).
• This talk will discuss how well we can determine the RGWs by the CMB observations.
The choice of pivot wavenumber
Ground-based Experiments• Ground-based experiments can well detect the CMB polarization by
observing a small part of full sky for a long time.
• In the near future, there are several ground-based experiments will begin to works, including QUad, BICEP, POLARBERA, QUIET, ClOVER, QUIJOTE, ACTPOL, SPTPOL, QUBIC and so on.
• The instrumental noises of the experiments in the near future are very close to the cosmic lensing limit.
• In addition to the space-based Planck satellites and the various ground-based experiments, some balloon-borne experiments (EBEX, PIPER, Spider). They have the similar detection ability as the ground-based experiments.
Planck or ground-based experiment?
Difference of Planck and Ground-based Experiments
• If detectable, Planck can only detect the reionization peak at l~6.
• Ground-based (or balloon-borne) experiments can only detect the recombination peak at l~100.
• CMBPol will detect both peaks!
Planck + PolarBear
(WZ & Zhang 2009)
Planned CMBPol (COrE, LiteBird) experiment
(see CMBPol white book for details)
(WZ, 2011)
CMBPol------ instrumental noises + lensing
CMBPol------ foregrounds
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:
(WZ & Baskaran 2009)
Testing inflationary consistency relations(WZ & Huang, 2011)
Single-field slow-roll inflations• consistency relation
• Results: r > 0.14 for EPIC-2m r > 0.06 for Ideal
Potential-driven G-inflations
Conclusions• The CMB observations provide an excellent opportunity to determine
the RGWs.
• We have derived the analytic formulae for: best-pivot wavenumber; signal-to-noise ratio and uncertainty of nt.
• The uncertainties of r and nt strongly depends on the cosmic reionization, especially for nt.
• Ignoring the foreground contaminations, Planck: nt~0.25 for r=0.1.△ Ideal: nt~0.007 for r=0.1△• The inflationary consistency relations are quite difficult to be tested.
Thank you!