Saving the invisible axion

Paul J. Steinhardt, Michaek S. Turner

Research output: Contribution to journalArticlepeer-review

162 Scopus citations


Recently it has been shown that the energy density contributed today by coherent oscillations of the invisible axion field corresponds to Ω {reversed tilde equals} 0.1 ( f{hook}a 1012 GeV) 11 9 (f{hook}a is the scale of peccei-Quinn SSB), apparently ruling out f{hook}a ≳ O(1013 GeV). We propose a simple way to avoid this bound: entropy production when the temperature of the universe is between about 1 GeV and 1 MeV. The entropy might be produced by a first-order phase transition, or the out-of-equilibrium decays of a relic particle species. For f{hook}a {reversed tilde equals} 1015 GeV, the entropy of the universe must be increased by a factor of O(102-103) to have Ωa {reversed tilde equals} O(1). If inflation also occurs at a temperature {reversed tilde equals}1015 GeV, then the de Sitter space produced fluctuations in the axion field lead to a Zel'dovich-like spectrum of (isothermal) perturbations in the axion energy density, with amplitude about 10-4. It has recently been argued that in an axion-dominated universe such a spectrum could lead to the formation of of the structure observed in the universe today.

Original languageEnglish (US)
Pages (from-to)51-56
Number of pages6
JournalPhysics Letters B
Issue number1-2
StatePublished - Sep 15 1983
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics


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