We identify a new cosmological problem for models which solve the strong CP puzzle with an invisible axion, unrelated to the domain wall problem. Because the axion is very weakly coupled, the energy density stored in the oscillations of the classical axion field does not dissipate rapidly; it exceeds the critical density needed to close the universe unless fa ≤ 1012 GeV, where fa is the axion decay constant. If this bound is saturated, axions may comprise the dark matter of the universe.
ASJC Scopus subject areas
- Nuclear and High Energy Physics