Constraints on active-sterile neutrino mixing from primordial abundances

Starting from the calculation of the neutrino distribution function, as a function of the active-sterile neutrino mixing parameters, we calculate primordial abundances of light nuclei (D, He-4, and Li-7) using a modified version of Kawano's code. The active-sterile neutrino mixing parameters and the baryon-to-photon ratio (eta(B)) enter the calculation as free parameters. By using the observational data of D, He-4, and Li-7, we set constraints on eta(B) and on the active-sterile neutrino mixing parameters. It is found that the value for the baryon-to-photon ratio depends strongly on the inclusion of Li-7 data in the sample, while the value for the mixing angles remain small.