Constraining Axion Inflation with Gravitational Waves across 29 Decades in Frequency

Peter Adshead, John T. Giblin, Mauro Pieroni, Zachary J. Weiner

Research output: Contribution to journalArticlepeer-review


We demonstrate that gravitational waves generated by efficient gauge preheating after axion inflation generically contribute significantly to the effective number of relativistic degrees of freedom Neff. We show that, with existing Planck limits, gravitational waves from preheating already place the strongest constraints on the inflaton's possible axial coupling to Abelian gauge fields. We demonstrate that gauge preheating can completely reheat the Universe regardless of the inflationary potential. Further, we quantify the variation of the efficiency of gravitational wave production from model to model and show that it is correlated with the tensor-to-scalar ratio. In particular, when combined with constraints on models whose tensor-to-scalar ratios would be detected by next-generation cosmic microwave background experiments, r≳10-3, constraints from Neff will probe or rule out the entire coupling regime for which gauge preheating is efficient.

Original languageEnglish (US)
Article number171301
JournalPhysical review letters
Issue number17
StatePublished - May 1 2020
Externally publishedYes

ASJC Scopus subject areas

  • General Physics and Astronomy


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