Axions, inflation and the anthropic principle
Katherine J. Mack; Katherine J. Mack; Kavli Institute for Cosmology, Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, U.K.
Журнал:
Journal of Cosmology and Astroparticle Physics
Дата:
2011-07-01
Аннотация:
The QCD axion is the leading solution to the strong-CP problem, a dark matter candidate, and a possible result of string theory compactifications. However, for axions produced before inflation, symmetry-breaking scales of f<sub>a</sub>≳10<sup>12</sup> GeV (which are favored in string-theoretic axion models) are ruled out by cosmological constraints unless both the axion misalignment angle θ<sub>0</sub> and the inflationary Hubble scale H<sub>I</sub> are extremely fine-tuned. We show that attempting to accommodate a high-f<sub>a</sub> axion in inflationary cosmology leads to a fine-tuning problem that is worse than the strong-CP problem the axion was originally invented to solve. We also show that this problem remains unresolved by anthropic selection arguments commonly applied to the high-f<sub>a</sub> axion scenario.
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