Gravitational wave forest from string axiverse

Naoya Kitajima, Jiro Soda, Yuko Urakawa

Research output: Contribution to journalArticlepeer-review

37 Citations (Scopus)


Axions predicted in string theory may have a scalar potential which has a much shallower potential region than the conventional cosine potential. We first show that axions which were located at such shallow potential regions generically undergo prominent resonance instabilities: the well-known narrow resonance and/or the flapping resonance, which has not been well investigated. We also study non-linear dynamics of axions caused by these resonance instabilities based on lattice simulation. We find that string axions in various mass ranges generate gravitational waves (GWs) with peaks at various frequencies determined by the mass scales, dubbed the GW forest. This may allow us to explore string axiverse through future multi-frequency GW observations. We also investigate GWs produced by the axion which accounts for present dark matter component.

Original languageEnglish
Article number008
JournalJournal of Cosmology and Astroparticle Physics
Issue number10
Publication statusPublished - 2018 Oct 4
Externally publishedYes


  • axions
  • gravitational waves/theory
  • physics of the early universe

ASJC Scopus subject areas

  • Astronomy and Astrophysics


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