Estimates of the cosmological axion density
Aug, 19915 pages
Published in:
- Phys.Lett.B 275 (1992) 279-283
- Published: 1992
Report number:
- LANCS-TH-17-91
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Abstract: (Elsevier)
In the scenario where the temperature in the early universe is high enough to restore the Peccei-Quinn symmetry, previous estimates of the axion mass density are reconsidered. The axion contribution to the density parameter is of the form Ω a =K( f a 10 12 GeV ) 1.2 where f a 2 is the vacuum value of the magnitude of the Peccei-Quinn field. If axions radiated by strings are ignored, or if they have a flat spectrum as advocated by Harari and Sikivie, K∼kγ 7 6 , where γ −1 <1 is the string spacing in Hubble units and k ≅1–10. If their spectrum is peaked at frequency γ t as advocated by Davis, K∼10kγ 7 6 . If γ ∼1, the first estimate is in essential agreement with earlier ones but the second is a factor of 7 smaller, which widens the allowed window for f a . These estimates include only the axions coming from oscillations of the axion field between the walls. In addition there are axions radiated by the walls, whose relative contribution to K is of order r 3 2 in the first case and 0.1r 3 2 in the second case, r being the time of wall annihilation divided by the time of wall formation. It could dominate, and close the axion window, if the walls survive for many Hubble times.- astrophysics
- postulated particle: axion
- axion: density
- radiation: axion
- axion: oscillation
- numerical calculations
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