Lyman-alpha transfer in primordial hydrogen recombination

Understand

Cosmological constraints from the cosmic microwave background (CMB) anisotropies rely on accurate theoretical calculations of the cosmic recombination history.

• Recent work has emphasized the importance of radiative transfer calculations due to the high optical depth in the HI Lyman lines.
• Transfer in the Lyman-alpha line is dominated by true emission and absorption, Hubble expansion, and resonant scattering.
• Resonant scattering causes photons to diffuse in frequency due to random kicks from the thermal velocities of hydrogen atoms, and also to drift toward lower frequencies due to energy loss via atomic recoil.