Detecting the cosmological recombination signal from space

TL;DR

This paper forecasts the potential for future space-based satellite experiments to detect the faint cosmological recombination lines in the CMB spectrum, which can confirm the universe's recombination history and refine cosmological parameters.

Contribution

It provides a detailed forecast for detecting recombination signals with future satellites, emphasizing their importance for cosmology and the feasibility with upcoming technology.

Findings

Recombination lines are detectable as tiny deviations in the CMB spectrum.

Future space experiments could confirm the recombination history.

Detecting these signals can improve cosmological parameter estimation.

Abstract

Spectral distortions of the CMB have recently experienced an increased interest. One of the inevitable distortion signals of our cosmological concordance model is created by the cosmological recombination process, just a little before photons last scatter at redshift $z\simeq 1100$. These cosmological recombination lines, emitted by the hydrogen and helium plasma, should still be observable as tiny deviation from the CMB blackbody spectrum in the cm--dm spectral bands. In this paper, we present a forecast for the detectability of the recombination signal with future satellite experiments. We argue that serious consideration for future CMB experiments in space should be given to probing spectral distortions and, in particular, the recombination line signals. The cosmological recombination radiation not only allows determination of standard cosmological parameters, but also provides a direct observational confirmation for one of the key ingredients of our cosmological model: the cosmological recombination history. We show that, with present technology, such experiments are futuristic but feasible. The potential rewards won by opening this new window to the very early universe could be considerable.