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: Sigma m(nu) < 0.40 eV at 99.9% C.L.; that extra massless particles have abundance Delta N-nu = 2 +/- 1 if freely streaming and Delta N-nu = 0 +/- 1.3 if interacting; that three interacting neutrinos are disfavoured at about 4 sigma. 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.