Blocking Active-Sterile Neutrino Oscillations in the Early Universe with a Majoron Field

We propose a new mechanism to block the active-sterile neutrino oscillations in the Early Universe. We show that a typical consequence of theories where the lepton number is spontaneously broken is the existence of a coherent cosmologic Majoron field with strength proportional to the lepton and baryon numbers of the Universe. This field interacts with leptons and changes the potentials relevant for neutrino oscillations. If the scale of lepton number symmetry breaking is of the order of 1 GeV then, a Majoron field and lepton number asymmetry of the order of the baryon asymmetry is strong enough to block the active-sterile neutrino oscillations with an atmospheric neutrino mass gap which otherwise, would bring the sterile neutrino into equilibrium at the BBN epoch. PACS numbers: 14.80.Mz, 14.60.Pq, 98.80.Ft, 95.30.-k