Shining ALP Dark Radiation

Abstract

String scenarios typically not only predict axion-like particles (ALPs) but also significant amounts of ALP dark radiation originating from the decay of the inflaton or a more general modulus. In this paper, we study the decay of such non-thermally produced relativistic (but massive) ALPs to photons. If the ALPs are sufficiently highly energetic, contribute to $\Delta N_{\mathrm{eff}}\gtrsim \mathcal{O}(0.001)$ and have a mass $m_a\gtrsim$ MeV we find that, using observations of X-, and $\gamma$-rays, the CMB and BBN, very small values of the ALP-photon coupling can be probed, corresponding to an origin of this coupling at the string (or even Planck) scale.

12 pages, 10 figures

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Cited by in corpus (7)

• Anisotropic cosmic optical background bound for decaying dark matter in light of the LORRI anomaly
• Axions in String Theory $-$ Slaying the Hydra of Dark Radiation
• Indirect Detection of eV Dark Matter via Infrared Spectroscopy
• High Energy Sphalerons for Baryogenesis at Low Temperatures
• Phenomenology of CP-even ALP
• Superheavy dark matter from the natural inflation in light of the highest-energy astroparticle events
• Searching for relativistic axions in the sky