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RECFAST: Calculate the Recombination History of the Universe

Posted: Thu Jun 30, 2011 10:56 am
by owlice
RECFAST: Calculate the Recombination History of the Universe

Abstract: RECFAST calculates the recombination of H, HeI, and HeII in the early Universe; this involves a line-by-line treatment of each atomic level. It differs in comparison to previous calculations in two major ways: firstly, the ionization fraction x_e is approximately 10% smaller for redshifts <~800, due to non-equilibrium processes in the excited states of H, and secondly, HeI recombination is much slower than previously thought, and is delayed until just before H recombines. RECFAST enables fast computation of the ionization history (and quantities such as the power spectrum of CMB anisotropies which depend on it) for arbitrary cosmologies.

Credit: Seager, Sara; Sasselov, Dimitar D.; Scott, Douglas

Site: https://www.cfa.harvard.edu/~sasselov/rec/
http://adsabs.harvard.edu/abs/1999ApJ...523L...1S

Bibcode: 2011ascl.soft06026S

ID: ascl:1106.026

Re: RECFAST: Calculate the Recombination History of the Universe

Posted: Sun Sep 04, 2016 7:35 pm
by owlice
Replaced non-working site link http://www.astro.ubc.ca/people/scott/recfast.html with https://www.cfa.harvard.edu/~sasselov/rec/ and edited abstract; original abstract appears below.

We have developed an improved recombination calculation of H, HeI, and HeII in the early Universe which involves a line-by-line treatment of each atomic level. We find two major differences compared with previous calculations. Firstly, the ionization fraction x_e is approximately 10% smaller for redshifts <~800, due to non-equilibrium processes in the excited states of H. Secondly, HeI recombination is much slower than previously thought, and is delayed until just before H recombines. We describe the basic physics behind the new results and present a simple way to reproduce our calculation. This should enable fast computation of the ionization history (and quantities such as the power spectrum of CMB anisotropies which depend on it) for arbitrary cosmologies, without the need to consider the hundreds of atomic levels used in our complete model.