Cosmology of neutrinos and extra-light particles after WMAP3

We study how present data probe standard and non-standard properties of neutrinos and the possible existence of new light particles, freely streaming or interacting, among themselves or with neutrinos. Our results include: \sum m_\nu \lt 0.40~\mathrm

{eV} at 99.9% C.L.; that extra massless particles have abundance ΔN_ν = 2 ± 1 if freely streaming and ΔN_ν = 0 ± 1.3 if interacting; that three interacting neutrinos are disfavoured at about 4σ. We investigate the robustness of our results by fitting different subsets of data. We developed our own cosmological computational tools, somewhat different from the standard ones.