New constraints on neutrino masses from cosmology

By combining data from cosmic microwave background (CMB) experiments (including the recent WMAP third year results), large scale structure (LSS) and Lyman-alpha forest observations, we derive upper limits on the sum of neutrino masses of Sigma m(v) < 0.17 eV at 95% c.l. We then constrain the hypothesis of a fourth, sterile, massive neutrino. For the third massless +1 massive neutrino case we bound the mass of the sterile neutrino to m(s) < 0.26 eV at 95% c.l. These results exclude at high significance the sterile neutrino hypothesis as an explanation of the LSND anomaly. We then generalize the analysis to account for active neutrino masses which tightens the limit to m(s) < 0.23 eV and the possibility that the sterile abundance is not thermal. In the latter case, the constraints in the (mass, density) plane are non-trivial. For a mass of > 1 eV or < 0.05 eV the cosmological energy density in sterile neutrinos is always constrained to be omega(nu) < 0.003 at 95% c.l. However, for a sterile neutrino mass of similar to 0.25 eV, omega(nu) can be as large as 0.01. (c) 2006 Elsevier B.V. All rights reserved.