Gravitational wave and CMB probes of axion kination

Raymond T. Co, David Dunsky, Nicolas Fernandez, Akshay Ghalsasi, Lawrence J. Hall, Keisuke Harigaya, Jessie Shelton

Research output: Contribution to journalArticlepeer-review


Rotations of an axion field in field space provide a natural origin for an era of kination domination, where the energy density is dominated by the kinetic term of the axion field, preceded by an early era of matter domination. Remarkably, no entropy is produced at the end of matter domination and hence these eras of matter and kination domination may occur even after Big Bang Nucleosynthesis. We derive constraints on these eras from both the cosmic microwave background and Big Bang Nucleosynthesis. We investigate how this cosmological scenario affects the spectrum of possible primordial gravitational waves and find that the spectrum features a triangular peak. We discuss how future observations of gravitational waves can probe the viable parameter space, including regions that produce axion dark matter by the kinetic misalignment mechanism or the baryon asymmetry by axiogenesis. For QCD axion dark matter produced by the kinetic misalignment mechanism, a modification to the inflationary gravitational wave spectrum occurs above 0.01 Hz and, for high values of the energy scale of inflation, the prospects for discovery are good. We briefly comment on implications for structure formation of the universe.

Original languageEnglish (US)
Article number116
JournalJournal of High Energy Physics
Issue number9
StatePublished - Sep 2022


  • Beyond Standard Model
  • Cosmology of Theories beyond the SM
  • Supersymmetric Standard Model

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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