English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

If the Peccei-Quinn symmetry associated to an axion has ever been restoredafter inflation, axion strings inevitably produce a contribution to thestochastic gravitational wave background. Combining effective field theoryanalysis with numerical simulations, we show that the resulting gravitationalwave spectrum has logarithmic deviations from a scale invariant form with anamplitude that is significantly enhanced at low frequencies. As a result, asingle ultralight axion-like particle with a decay constant larger than$10^{14}~{\rm GeV}$ and any mass between $10^{-18}~{\rm eV}$ and $10^{-28}~{\rmeV}$ leads to an observable gravitational wave spectrum and is compatible withconstraints on the post-inflationary scenario from dark matter overproduction,isocurvature and dark radiation. Since the spectrum extends over a wide rangeof frequencies, the resulting signal could be detected by multiple experiments.We describe straightforward ways in which the Peccei-Quinn symmetry can berestored after inflation for such decay constants. We also comment on therecent possible NANOgrav signal in light of our results.

Observing Invisible Axions with Gravitational Waves