Cosmology with Rayleigh scattering
Beyond primary CMB with the next generation of surveys
Benjamin Beringue with Daan Meerburg, Nick Battaglia, Joel Meyers 11/08/2020 1 CMB-S4 2020 Cosmology with Rayleigh scattering
Outline :
• Distortions induced by Rayleigh scattering
• Detectability with the next generation of CMB surveys
• Impact on cosmological parameters
• Effort in component separation
11/08/2020 CMB-S4 2020 2 Cosmology with Rayleigh scattering
Around recombination, photons are kept in equilibrium with the plasma by two scattering processes :
Thomson scattering: Rayleigh scattering:
- Off free electrons - Off neutral species (Hydrogen, Helium, …) - Frequency independent - Frequency dependent � - Cross section � - Cross section �� ∝ � � � e- e- p+
11/08/2020 CMB-S4 2020 3 Cosmology with Rayleigh Scattering
Redshift z 1693 1269 1088 804 666
Thomson scattering Rayleigh Scattering 750Ghz For Rayleigh scattering to Rayleigh Scattering 500Ghz become effective, enough neutral species have to be present.
After recombination, neutral Visibility species will dilute ∝ � and photons will redshift ∝ � .
200.0 250.0 280.7 350.0 400.0 Conformal time ¥ [Mpc] [BB et al. 2020 : 2008.xxxx]
11/08/2020 CMB-S4 2020 4 Cosmology with Rayleigh scattering
Rayleigh scattering increases the comoving opacity of the plasma and makes it frequency dependent :
�̇ = ��!�" → �̇ � = ��!�" + � �# + 0.1 �#! �$(�) This leads to :
- A damping of small scales anisotropies both in temperature and E-mode polarization. - On large angular scales, the shift of the last scattering surface towards lower redshifts, where the local quadrupole is larger, boosts the large scales E-mode signal. - A shift in the location of the acoustic peaks, both in temperature and E-mode polarization spectra.
12/08/2020 CMB-S4 2020 5 Cosmology with Rayleigh scattering
Rayleigh scattering effects at frequencies below ∼ 700 GHz can be modelled as a linear distortion to the primary CMB :