Axion as a cold dark matter candidate
Abstract
Here we generally prove that the axion as a coherently oscillating scalar field acts as a cold dark matter in nearly all cosmologically relevant scales. The proof is made in the linear perturbation order. Compared with our previous proof based on solutions, here we compare the equations in the axion with the ones in the cold dark matter, thus expanding the valid range of the proof. Deviation from purely pressureless medium appears in very small scale where axion reveals a peculiar equation of state. Our analysis is made in the presence of the cosmological constant, and our conclusions are valid in the presence of other fluid and field components.
- Publication:
-
Physics Letters B
- Pub Date:
- September 2009
- DOI:
- 10.1016/j.physletb.2009.08.031
- arXiv:
- arXiv:0902.4738
- Bibcode:
- 2009PhLB..680....1H
- Keywords:
-
- 14.80.Mz;
- 95.35.+d;
- 98.80.Jk;
- 98.80.-k;
- Axions and other Nambu-Goldstone bosons;
- Dark matter;
- Mathematical and relativistic aspects of cosmology;
- Cosmology;
- Astrophysics - Cosmology and Extragalactic Astrophysics;
- General Relativity and Quantum Cosmology;
- High Energy Physics - Phenomenology;
- High Energy Physics - Theory
- E-Print:
- 4 pages, no figure