Observing invisible axions with gravitational waves



Gorghetto, Marco, Hardy, Edward ORCID: 0000-0003-3263-6575 and Nicolaescu, Horia
(2021) Observing invisible axions with gravitational waves. JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 2021 (6). 034-034.

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Abstract

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

Item Type: Article
Additional Information: 39 pages + appendices
Uncontrolled Keywords: axions, Cosmic strings, domain walls, monopoles, gravitational waves / theory, cosmology of theories beyond the SM
Depositing User: Symplectic Admin
Date Deposited: 11 Feb 2021 11:12
Last Modified: 18 Jan 2023 23:00
DOI: 10.1088/1475-7516/2021/06/034
Open Access URL: https://iopscience.iop.org/article/10.1088/1475-75...
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3115485