The primordial information content of Rayleigh Anisotropies

Understand

Anisotropies in the cosmic microwave background (CMB) are primarily generated by Thomson scattering of photons by free electrons.

• Around recombination, the Thomson scattering probability quickly diminishes as the free electrons combine with protons to form neutral hydrogen off which CMB photons can scatter through Rayleigh scattering.
• Unlike Thomson scattering, Rayleigh scattering is frequency dependent resulting in the generation of anisotropies with a different spectral dependence.
• Unfortunately the Rayleigh scattering efficiency rapidly decreases with the expansion of the neutral universe, with the result that only a small percentage of photons are scattered by neutral hydrogen.