A simple model for spectral swapping of supernova neutrinos

Neutrinos emitted from a core-collapse supernova can experience collective flavor transformation because of high neutrino fluxes. As a result, neutrinos of different flavors can have their energy spectra (partially) swapped, a phenomenon known as the (stepwise) spectral swapping or spectral split. We give a brief review of a simple model that explains this phenomenon.