Rayleigh scattering: blue sky thinking for future CMB observations

Understand

Rayleigh scattering from neutral hydrogen during and shortly after recombination causes the CMB anisotropies to be significantly frequency dependent at high frequencies.

• This may be detectable with Planck, and would be a strong signal in any future space-based CMB missions.
• The later peak of the Rayleigh visibility compared to Thomson scattering gives an increased large-scale CMB polarization signal that is a greater than 4% effect for observed frequencies greater than 500GHz.
• There is a similar magnitude suppression on small scales from additional damping.