Primordial helium recombination II: two-photon processes

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dc.creatorHirata, Christopher M.
dc.creatorSwitzer, Eric R.
dc.date2007-02-06
dc.date.accessioned2026-07-07T11:42:45Z
dc.date.available2026-07-07T11:42:45Z
dc.descriptionInterpretation of precision measurements of the cosmic microwave background (CMB) will require a detailed understanding of the recombination era, which determines such quantities as the acoustic oscillation scale and the Silk damping scale. This paper is the second in a series devoted to the subject of helium recombination, with a focus on two-photon processes in He I. The standard treatment of these processes includes only the spontaneous two-photon decay from the 2^1S level. We extend this treatment by including five additional effects, some of which have been suggested in recent papers but whose impact on He I recombination has not been fully quantified. These are: (i) stimulated two-photon decays; (ii) two-photon absorption of redshifted HeI line radiation; (iii) two-photon decays from highly excited levels in HeI (n^1S and n^1D, with n>=3); (iv) Raman scattering; and (v) the finite width of the 2^1P^o resonance. We find that effect (iii) is highly suppressed when one takes into account destructive interference between different intermediate states contributing to the two-photon decay amplitude. Overall, these effects are found to be insignificant: they modify the recombination history at the level of several parts in 10^4.
dc.description19 pages, 11 figures, to be submitted to PRD
dc.identifierhttps://arxiv.org/abs/astro-ph/0702144
dc.identifierhttp://arxiv.org/abs/astro-ph/0702144
dc.identifierPhys.Rev.D77:083007,2008
dc.identifierdoi:10.1103/PhysRevD.77.083007
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/200998
dc.subjectAstrophysics
dc.titlePrimordial helium recombination II: two-photon processes
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