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arXiv · 1602.08433

Reionization during the dark ages from a cosmic axion background

Carmelo Evoli·Matteo Leo·Alessandro Mirizzi·Daniele Montanino
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Abstract

Recently it has been pointed out that a cosmic background of relativistic axion-like particles (ALPs) would be produced by the primordial decays of heavy fields in the post-inflation epoch, contributing to the extra-radiation content in the Universe today. Primordial magnetic fields would trigger conversions of these ALPs into sub-MeV photons during the dark ages. This photon flux would produce an early reionization of the Universe, leaving a significant imprint on the total optical depth to recombination $\tau$. Using the current measurement of $\tau$ and the limit on the extra-radiation content $\Delta N_{\rm eff} $ by the Planck experiment we put a strong bound on the ALP-photon conversions. Namely we obtain upper limits on the product of the photon-ALP coupling constant $g_{a\gamma}$ times the magnetic field strength $B$ down to $g_{a\gamma} B \gtrsim 6 \times 10^{-18} \textrm{GeV}^{-1} \textrm{nG} $ for ultralight ALPs.

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Carmelo Evoli, Matteo Leo, Alessandro Mirizzi, Daniele Montanino. 2016-02-26. Reionization during the dark ages from a cosmic axion background. https://doi.org/10.1088/1475-7516%2F2016%2F05%2F006

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