Abstract. I discuss BBN with late electron-sterile neutrino oscillations, effective after electron neutrino freezing. The primordial production of ⁴He in the presence of oscillations is numerically calculated for different initial population of the sterile neutrino 0 ≤ δN_s < 1. General BBN bounds on oscillation parameters are presented, corresponding to ~ 5% overproduction of the primordial ⁴He and different initial population of the sterile neutrino, namely δN_s=0; 0.5; 0.7; 0.9. The cosmological constraints corresponding to initially partially filled sterile state are relaxed, compared to the case of initially zero population of the sterile neutrino.

Full-text: PDF