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New cosmological mass limit on thermal relic axions

S. Hannestad·A. Mirizzi·G. Raffelt
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Abstract

Observations of the cosmological large-scale structure provide well-established neutrino mass limits. We extend this argument to thermal relic axions. We calculate the axion thermal freeze-out temperature and thus their cosmological abundance on the basis of their interaction with pions. For hadronic axions we find a new mass limit $m_a<1.05$ eV (95% CL), corresponding to a limit on the axion decay constant of $f_a>5.7\times 10^6$ GeV. For other models this constraint is significantly weakened only if the axion-pion coupling is strongly suppressed. For comparison we note that the same approach leads to $\sum m_ν<0.65$ eV (95% CL) for neutrinos.

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S. Hannestad, A. Mirizzi, G. Raffelt. 2005-04-07. New cosmological mass limit on thermal relic axions. https://doi.org/10.1088/1475-7516%2F2005%2F07%2F002

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