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Determination of tensor spectral index in the CMB

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.

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Determination of tensor spectral index in the CMB

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  1. Determination of tensor spectral index in the CMB Wen Zhao @ IHEP . 2012

  2. 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. • 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.

  3. The choice of pivot wavenumber

  4. Ground-based Experiments • Ground-based experiments can well detect the CMB polarization by observinga small part of full sky for a long time. • In the near future, there are several ground-based experiments will begin to works, includingQUad, 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 thecosmic lensing limit. • In addition to the space-based Planck satellites and the various ground-based experiments, someballoon-borneexperiments (EBEX, PIPER, Spider). They have the similar detection ability as the ground-based experiments.

  5. Planckorground-based experiment?

  6. 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!

  7. Planck + PolarBear (WZ & Zhang 2009)

  8. Planned CMBPol (COrE, LiteBird) experiment (see CMBPol white book for details) (WZ, 2011)

  9. CMBPol------ instrumental noises + lensing

  10. CMBPol------ foregrounds

  11. 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) Ideal CMB experiment

  12. Testing inflationary consistency relations(WZ & Huang, 2011)

  13. Single-field slow-roll inflations • consistency relation • Results: r > 0.14 for EPIC-2m r > 0.06 for Ideal

  14. Potential-driven G-inflations

  15. 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.

  16. Thank you!

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