Primordial helium recombination. II. Two-photon processes

Journal Article · Tue Apr 15 04:00:00 EDT 2008 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.77.083007· OSTI ID:21249994

Hirata, Christopher M; Switzer, Eric R ^[1]

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1. School of Natural Sciences, Institute for Advanced Study, Princeton, New Jersey 08540 (United States)

Interpretation 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{sup 1}S 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 He i line radiation; (iii) two-photon decays from highly excited levels in He i (n{sup 1}S and n{sup 1}D, with n{>=}3); (iv) Raman scattering; and (v) the finite width of the 2{sup 1}P{sup 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{sup 4}.

• OSTI ID: 21249994
• Journal Information: Physical Review. D, Particles Fields, Journal Name: Physical Review. D, Particles Fields Journal Issue: 8 Vol. 77; ISSN PRVDAQ; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
DECAY
DECAY AMPLITUDES
EXCITED STATES
HELIUM
INTERFERENCE
INTERMEDIATE STATE
MULTI-PHOTON PROCESSES
OSCILLATIONS
PHOTONS
RAMAN EFFECT
RECOMBINATION
RELICT RADIATION
RESONANCE