Opening the 1 Hz axion window

David J.E. Marsh, Wen Yin

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


An axion-like particle (ALP) with mass mϕ ∼ 10−15 eV oscillates with frequency ∼1 Hz. This mass scale lies in an open window of astrophysical constraints, and appears naturally as a consequence of grand unification (GUT) in string/M-theory. However, with a GUT-scale decay constant such an ALP overcloses the Universe, and cannot solve the strong CP problem. In this paper, we present a two axion model in which the 1 Hz ALP constitutes the entirety of the dark matter (DM) while the QCD axion solves the strong CP problem but contributes negligibly to the DM relic density. The mechanism to achieve the correct relic densities relies on low-scale inflation (mϕ ≲ Hinf ≲ 1 MeV), and we present explicit realisations of such a model. The scale in the axion potential leading to the 1 Hz axion generates a value for the strong CP phase which oscillates around θ¯ QCD∼ 10 − 12, within reach of the proton storage ring electric dipole moment experiment. The 1 Hz axion is also in reach of near future laboratory and astrophysical searches.

Original languageEnglish
Article number169
JournalJournal of High Energy Physics
Issue number1
Publication statusPublished - 2021 Jan


  • Beyond Standard Model
  • CP violation
  • Cosmology of Theories beyond the SM
  • M-Theory


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