Abstract. The small-scale power spectrum of the cosmological matter distribution, together with other cosmological data, provides a sensitive measure of the hot dark matter fraction, leading to restrictive neutrino mass limits. We extend this argument to generic cases of low-mass thermal relics. We vary the cosmic epoch of thermal decoupling, the radiation content of the universe, and the new particle's spin degrees of freedom. Our treatment covers various scenarios of active plus sterile neutrinos or axion-like particles. For three degenerate massive neutrinos, we reproduce the well-known limit of m_ν<0.34 eV. In a 3+1 scenario of 3 massless and 1 fully thermalized sterile neutrinos we find m_ν<1.0 eV. Thermally produced QCD axions must obey m_a<3.0 eV, superseding limits from a direct telescope search, but leaving room for solar eV-mass axions to be discovered by the CAST experiment.

Key words: dark matter; cosmological neutrinos; axions

E-print number: hep-ph/0312154
Cited: by
Refers: to

Received 3 February 2004, accepted for publication 14 April 2004
Published 29 April 2004