Contrary to charged lepton degeneracies which are tightly constrained by the measured baryon-to-photon ratio, the allowed values of the primordial neutrino asymmetries cover a large range. In order to study the evolution of these asymmetries in the early Universe, one needs to solve a set of quantum kinetic equations that include vacuum mixing effects, mean-field potentials and collisions (scattering and annihilations with charged leptons and among (anti)neutrinos), which represents a genuine numerical challenge.
In this talk, I will present the results of a complete three-flavour calculation with the full collision term (which was always approximated in previous numerical studies) at the epoch of neutrino decoupling, while laying emphasis on an effective description of neutrino oscillations that corresponds to averaging over the shortest time scale. In addition to reducing the computation time while preserving the accuracy of the results, this “Adiabatic Transfer of Averaged Oscillations” (ATAO) approximation provides a consistent framework to understand the origin of the so-called synchronous oscillations. Moreover, it leads to new results, such as the existence of a regime of faster oscillations when the self-interaction mean-field domination dwindles.
