Fast flavor evolution in dense neutrino systems, as described in quantum field theory

Investigations of dense neutrino cloud evolution through quantum kinetic equations led to the possibility of ``fast flavor'' (FF) processes. It is shown here that the usual quantum kinetic equations, while signaling the instabilities that make some instances of FF possible, are being erroneously interpreted. Approaching the subject directly from the quantum field theory that defines the standard model shows the computational structures in most of the recent FF literature to be completely invalid. Our revisions also underlie what promise to be new early Universe applications and a general result for relic supernova neutrinos that could be tested as a feature of the diffuse neutrino spectrum.