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 ma<1.05 eV (95% CL), corresponding to a limit on the axion decay constant of fa>5.7×106 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 ∑mν<0.65 eV (95% CL) for neutrinos.
@article{arxiv.hep-ph/0504059,
title = {New cosmological mass limit on thermal relic axions},
author = {S. Hannestad and A. Mirizzi and G. Raffelt},
journal= {arXiv preprint arXiv:hep-ph/0504059},
year = {2008}
}