Tensor non-Gaussianity from axion-gauge-fields dynamics: Parameter search

Aniket Agrawal, Tomohiro Fujita, Eiichiro Komatsu

Research output: Contribution to journalArticlepeer-review

40 Citations (Scopus)


We calculate the bispectrum of scale-invariant tensor modes sourced by spectator SU(2) gauge fields during inflation in a model containing a scalar inflaton, a pseudoscalar axion and SU(2) gauge fields. A large bispectrum is generated in this model at tree-level as the gauge fields contain a tensor degree of freedom, and its production is dominated by self-coupling of the gauge fields. This is a unique feature of non-Abelian gauge theory. The shape of the tensor bispectrum is approximately an equilateral shape for 3lesssim mQlesssim 4, where mQ is an effective dimensionless mass of the SU(2) field normalised by the Hubble expansion rate during inflation. The amplitude of non-Gaussianity of the tensor modes, characterised by the ratio Bh/P2h , is inversely proportional to the energy density fraction of the gauge field. This ratio can be much greater than unity, whereas the ratio from the vacuum fluctuation of the metric is of order unity. The bispectrum is effective at constraining large mQ regions of the parameter space, whereas the power spectrum constrains small mQ regions.

Original languageEnglish
Article number027
JournalJournal of Cosmology and Astroparticle Physics
Issue number6
Publication statusPublished - 2018 Jun 18
Externally publishedYes


  • CMBR polarization
  • gravitational waves / sources
  • ination

ASJC Scopus subject areas

  • Astronomy and Astrophysics


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