Signals from the Early Universe

It is proposed to account for the time-dependent partial thermalization of the Ly α lines emitted during cosmic recombination of electrons and protons in the early Universe based on an analytically solvable nonlinear diffusion model. The amplitude of the partially thermalized and redshifted Lyα line is found to be too low to be visible in the cosmic microwave spectrum, in accordance with previous numerical models and Planck observations. New space missions with more sensitive spectrometers are required to detect Ly α-remnants from recombination as frequency fluctuations in the cosmic microwave background. (An extended version of this article has previously appeared in Scientific Reports).