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

Understand

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.