Axions, inflation and the anthropic principle
Abstract
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 fagtrsim1012 GeV (which are favored in string-theoretic axion models) are ruled out by cosmological constraints unless both the axion misalignment angle θ0 and the inflationary Hubble scale HI are extremely fine-tuned. We show that attempting to accommodate a high-fa 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-fa axion scenario.
- Publication:
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Journal of Cosmology and Astroparticle Physics
- Pub Date:
- July 2011
- DOI:
- 10.1088/1475-7516/2011/07/021
- arXiv:
- arXiv:0911.0421
- Bibcode:
- 2011JCAP...07..021M
- Keywords:
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- Astrophysics - Cosmology and Extragalactic Astrophysics;
- High Energy Physics - Phenomenology;
- High Energy Physics - Theory
- E-Print:
- 19 pages, 3 figures. Submitted to Phys Rev D