CMB Rayleigh New particles and Foregrounds contamination

Benjamin Beringue with Daan Meerburg and Joel Meyers

01/04/2019 CCAT-prime Workshop - Santiago de Chile 1 CMB Rayleigh Scattering : New particles and Foregrounds Contamination

Outline :

• What is Rayleigh Scattering ?

• What does this signal look like on the ?

• Can CCAT-prime detect it ?

• What can we do with it ?

01/04/2019 CCAT-prime Workshop - Santiago de Chile 2 CMB Rayleigh Scattering : New particles and Foregrounds Contamination

What is Rayleigh Scattering ?

In the early universe : !

• Thomson Scattering couples photons with free electrons e-

!

• Rayleigh Scattering couples photons with neutral species e-

p+

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What is Rayleigh Scattering ?

The number of CMB photons that will experience Rayleigh Scattering reads :

Γ " = $% " × '(

(Frequency dependent) Rayleigh scattering : Fraction of neutral hydrogen , 3 4 " 638 " 1299667 " $% " = $) + + + … Photons can also scatter off neutral Helium but "*++ 243 "*++ 236196 "*++ given the relative abundance of He, it can be neglected.

• $) : Thomson scattering cross section : • "*++ ~ 3.1 × 10 ;<= See Lewis 2013 and Alipour et al. 2015

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What is Rayleigh Scattering ?

Thomson Scattering 1.2 z 1088 ⇡ Rayleigh Scattering

1.0 z 1014 ⇡ Hydrogen dilute as ∝ "#$ 0.8 Photons dilute as ∝ "#% So Rayleigh ∝ "#& 0.6 Visibility g(z) 0.4

Fraction of free electrons 0.2 Fraction of neutral hydrogen Last scattering surface 0.0 2500 2000 1500 1000 500 1300 1200 1100 1000 900 800 700 600 500 400 Redshift Not enough neutral hydrogen

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What does the signal look like?

104 102 103 • Rayleigh scattering is polarized in 100 102 ] ] 2 2 the same way as Thomson 1

10 µK 2 µK [ [ 10 ⇡ ⇡ 2 2 / Scattering. / 100 TT TE ` ` 4 C C 10 1 10 + 1) + 1) ` ` ( 2 ( 6 ` 10 ` 10

3 10 Primary auto-spectrum Primary auto-spectrum 8 Rayleigh auto-spectrum at 500Ghz 10 Rayleigh auto-spectrum at 500Ghz 4 • Can look for both Rayleigh auto- 10 Rayleigh x Primary cross-spectrum Rayleigh x Primary cross-spectrum spectra or its cross-correlation with

102 the Thomson Scattering signal 102

(Primary CMB) 100 100 ] ] 2 2 2 10 µK

µK 2 [ [ 10 ⇡ ⇡ 2 2 / / 4 ET EE ` 4 ` 10 C " 10 C + 1) • Cross spectra scale as ! and auto- + 1) ` ` 6 ( 6 ( 10 ` spectra as !#. 10 ` Primary auto-spectrum 8 Primary auto-spectrum 8 10 10 Rayleigh auto-spectrum at 500Ghz Rayleigh auto-spectrum at 500Ghz Rayleigh x Primary cross-spectrum Rayleigh x Primary cross-spectrum

See Lewis 2013 and Alipour et al. 2015 101 102 103 101 102 103 and Rayleigh version of CAMB. ` ` 01/04/2019 CCAT-prime Workshop - Santiago de Chile 6 CMB Rayleigh Scattering : New particles and Foregrounds Contamination

What does the signal look like?

Rayleigh Scattering signal is strongly correlated with the primary CMB.

100 Temperature E-mode On large scales : 75 [%] ⌫

• Temperature is uncorrelated, optical depths from R ⌫ 50 R Rayleigh is small compared to these modes. l C 0

• Polarization is sourced by the local quadrupole X 0 25 X that remains coherent on large scales and grows l between the two scattering surfaces, so signal is C q

/ 0 correlated. ⌫ R 0 X l

C 25 On small scales :

50 • Temperature is strongly (un-) correlated. Rayleigh scattering acts as an additional screening and 75 contributes to the damping of small scales. Correlation : • Similar in polarization. 100 101 102 103 01/04/2019 CCAT-prime Workshop - Santiago de Chile ` 7 CMB Rayleigh Scattering : New particles and Foregrounds Contamination

Can CCAT-prime detect it ? Rayleigh auto-spectra are too small to be detected by CCAT-p but its cross correlations could be.

0 1.00 270GHz 0.75 350Ghz 1 0.50 S/N Cross ` 0.25 C 2 ⇡ 0.00 2

/ 0 500 1000 1500 2000 2500 3000 3 1000

+ 1) 800 `

( 4 600 ⇤ 400 ` 270GHz 5 350GHz 200 0 Cumulative S/N 0 500 1000 1500 2000 2500 3000 500 1000 1500 2000 2500 3000 ` ` Assumptions : Sensitivities : 7.3$% − '()*+, @270 GHz, : 41$% − '()*+, @350 GHz rescaled to cover 10.000 deg3. Beams : 0.8 '()*+, @270GHz, : 0.6 '()*+, @350GHz. No foregrounds 01/04/2019 CCAT-prime Workshop - Santiago de Chile 8 CMB Rayleigh Scattering : New particles and Foregrounds Contamination

Can CCAT-prime detect it ? Foregrounds are a potential source of contamination. Their effect needs to be understood.

To mitigate foregrounds 140 Fiducial Noise only, no fg contamination, we use an Internal Residual noise bias 120 Linear Combination (ILC) method : Unbiased cross spectrum S/N ~ 180 100 Cross

- Take a linear combination of `

the different channels that C ⇡ 80 maximizes the CMB signal has 2 / explicitly no Rayleigh and 60

minimizes foregrounds and + 1) ` noise. ( 40 ⇤ `

- Similar for Rayleigh. 20

- Cross correlates the two. 0

500 1000 1500 2000 2500 3000 3500 See Remazeilles et al 2011. ` 01/04/2019 CCAT-prime Workshop - Santiago de Chile 9 CMB Rayleigh Scattering : New particles and Foregrounds Contamination

Can CCAT-prime detect it ? Foregrounds are a potential source of contamination. Their effect needs to be understood.

250 To mitigate foregrounds Fiducial Including CIB + contamination, we use an Internal Residual noise bias noise 200 Linear Combination (ILC) method : Unbiased cross spectrum S/N ~ 80 - Take a linear combination of 150 Cross the different channels that ` C

maximizes the CMB signal has ⇡ 2 explicitly no Rayleigh and / 100 minimizes foregrounds and + 1) `

noise. ( 50 ⇤ ` - Similar for Rayleigh.

0 - Cross correlates the two.

50 See Remazeilles et al 2011. 500 1000 1500 2000 2500 3000 3500 01/04/2019 CCAT-prime Workshop - Santiago de Chile ` 10 CMB Rayleigh Scattering : New particles and Foregrounds Contamination

What can we do with it ? If Rayleigh scattering signal is detected, it could be used for several purposes :

• Very efficient probe of recombination history, meaning better constraints on Helium fraction or example.

$ $ • Measuring the local expansion rate therefore better constraining densities Ω"ℎ , Ω%ℎ or even the number of relativistic species &'((.

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What can we do with it ?

Improvement on !"## from including Rayleigh scattering in a Fisher Forecast. 0.07000 (Ne↵) as a function of e↵ort Assumptions : Forecast for CCAT + SO + PLANCK : TT+TE+EE + Rayleigh Forecast for CCAT + SO + PLANCK : TT+TE+EE - CCAT-p on 10.000 deg2 : 270,350,405 GHz. ℓ%&' = 500, ℓ%,- = 5000 0.06000

- SO baseline on 40% of the sky from ℓ%&' = ) ↵ 0.05875 30 to ℓ = 5000. e

%,- N (

8% - PLANCK on 75% of the sky from ℓ%&' = 2 to 0.05409 ℓ%,- = 2500. 2.6 - No foregrounds 0.05000 ⇥

Detecting and using Rayleigh scattering would mean divide the integration time by 0.5 1.0 1.5 2.0 2.5 3.0 3.5 two to reach a similar sensitivity. Equivalent e↵ort (eg. number of detectors, integration time, ...)

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Conclusion

• Rayleigh Scattering is a very well understood and modelled mechanism however it hasn’t been observed.

• Its frequency dependence and correlation with the primary CMB are unique on the sky.

• CCAT-prime with its broad frequency coverage and low sensitivity is a unique set-up for a first detection.

• Including Rayleigh Scattering in a Fisher forecast shows non negligible improvement on !"##.

• Foregrounds are a source of contamination that need to be more carefully looked at but the signal seems to be recovered with a large signal to noise. Adding polarization should also help a lot since both atmosphere and foregrounds are less of an issue in polarization.

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Conclusion

Thanks a lot for your attention !

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