Avoiding BBN Constraints on Mirror Models for Sterile Neutrinos
  We point out that in models that explain the LSND result for neutrino oscillation using the mirror neutrinos, the big bang nucleosynthesis constraint can be avoided by using the late time phase transition that only helps to mix the active and the sterile neutrinos. We discuss the astrophysical as well as cosmological implications of this proposal. 
R. N. Mohapatra and S. Nasri