Synchronised neutrino oscillations from self interaction and associated applications

A recent revival of interest in synchronised oscillations due to neutrino–neutrino forward scattering in dense gases has led to two interesting applications with notable outcomes: (i) cosmological bounds on neutrino–antineutrino asymmetries are improved owing to flavour equilibration prior to the onset of big bang nucleosynthesis, and (ii) a neutron-rich environment required for $r$-process nucleosynthesis is shown to be always maintained in a supernova hot bubble irrespective of flavour oscillations, contrary to results from previous studies. I present in this talk a pedagogical review of these works.