1. On the detection of the tensor-to-scalar ratio r using the CMB B-modes
Agnès Ferté
In collaboration with: Julien Peloton, Julien Grain, Radek Stompor
Based on: arxiv:

2. CMB B-modes caused by tensor perturbations and lensing of E-modes
(Q,U) maps
E and B modes power spectra
Tensor-to-scalar ratio r

3. CMB B-modes at low-l probe the primordial Universe
Lensing B modes:
1st direct detection by Polarbear (arxiv: )
Primordial B modes:
r<0.12 (Bicep2/Keck + Planck)

4. Estimation of B modes power spectrum on a masked sky: the E-to-B leakage
Function of the mask
Mode counting variance
Standard estimation of B-modes
1 % of the sky
From Grain et al, 2009

5. Pure pseudo spectrum method (x2pure code)
+ optimisation of the window function
1 % of the sky
pure
mode counting
Other methods
Smith, 2006
Grain et al, 2009
Ferté et al, 2013
From Ferté et al, 2013

6. Pure pseudo spectrum method (x2pure code)
+ optimisation of the window function
71 % of the sky
Other methods
pure
mode counting
Smith, 2006
Grain et al, 2009
Ferté et al, 2013

7. Impact of leakage on the forecasts of CMB B modes detection?
1st investigation: ideal experiments
2nd investigation: 3 selected realistic experiments

8. Signal-to-noise ratio computed using Fisher matrix
Error on r
Covariance matrix computed using:
Mode counting variance =
Pure method = pure estimation + MC simulations

9. 1st approach: ideal small scale experiments1%
r=0.1

10. Mode-counting variance for optimal sky coverage
Optimal sky fraction

11. 2nd approach: 3 realistic experiments
Spec.
Small scale
Array of telescope
Satellite
Sky fraction 1%
36%
71%
Noise (muK-arcmin)
inhomogenesous (average of 5) 1 2
Beam (arcmin) 8 3
Dire que array de télescopes =study of window functions cause reach a limitation (in the noise)

12. Uncertainties on the power spectrum

13. Accessible r at 3σ detection
Example of satellite xp
mode counting
pure
Small scale xp
Telescopes array
Satellite mission
Mode counting
r > 0.038
r >
r >
Pure method
r > 0.11
r >
r >

14. Foreground impact on the detection of r
Remove the first bin: 2 < l < 20
Example of satellite xp
Small scale xp
Telescopes array
Satellite mission
Mode counting
r > 0.04
r >
r >
Pure method
r > 0.11
r >
r >

15. TO TAKE AWAY The pure estimation of B modes is awesome
The mode-counting approach is enough to state on optimal sky coverage
The pure method is mandatory to perform realistic forecasts on r detection
Potential future satellite mission: r ≥ 10-3 Stage 4 array of telescope: r ≥ 10-2
Current ground-based or balloon borne: r ≥ 10-1
Side ‘personal’ note: the CMB TB and EB correlations hold information on fundamental physics (e.g. : parity breaking, birefringence, primordial magnetic field…)

16. From NASA

17. Effect of binning

18. Optimised window functions

19. SNR on r
Small scale
Array of telescopes