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: at 99.9% C.L.; that extra massless particles have abundance ΔNν = 2 ± 1 if freely streaming and ΔNν = 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.