paper

Measuring the Primordial Deuterium Abundance During the Cosmic Dark Ages

arXiv:astro-ph/0505173 · doi:10.1103/PhysRevLett.97.091301

Abstract

We discuss how measurements of fluctuations in the absorption of cosmic microwave background (CMB) photons by neutral gas during the cosmic dark ages, at redshifts z ~ 7--200, could reveal the primordial deuterium abundance of the Universe. The strength of the cross-correlation of brightness-temperature fluctuations due to resonant absorption of CMB photons in the 21-cm line of neutral hydrogen with those due to resonant absorption of CMB photons in the 92-cm line of neutral deuterium is proportional to the fossil deuterium to hydrogen ratio [D/H] fixed during big bang nucleosynthesis (BBN). Although technically challenging, this measurement could provide the cleanest possible determination of [D/H], free from contamination by structure formation processes at lower redshifts, and has the potential to improve BBN constraints to the baryon density of the Universe Ω_{b} h^2. We also present our results for the thermal spin-change cross-section for deuterium-hydrogen scattering, which may be useful in a more general context than we describe here.

4 pages, 3 figures, submitted to Phys. Rev. Lett

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