Relaxed constraints on neutrino oscillation parameters
  We study the cosmological constraints on active-sterile neutrino oscillations nu_e <-> nu_s for the case when nu_s is partially filled initially, i.e. 0 < delta N_s < 1. We provide numerical analysis of the cosmological production of He-4, in the presence of nu_e <-> nu_s oscillations, effective after neutrino decoupling, accounting for all known oscillations effects on cosmological nucleosynthesis. Cosmological constraints on oscillation parameters corresponding to higher than 5% He-4 overproduction and different non-zero initial populations of the sterile state delta N_s < 1 are calculated. These generalized cosmological constraints corresponding to delta N_s > 0 are relaxed in comparison with the delta N_s = 0 case and the relaxation is proportional to delta N_s. 
Daniela P. Kirilova and Mariana P. Panayotova