Theory of Fast-Flavor Conversion of Supernova Neutrinos

Soumya Bhattacharyya 2022 Springer Proc. Phys. 277 621--625

A supernova natively emits neutrinos and antineutrinos of all flavors with
different luminosities and energy spectra. These neutrinos can undergo neutrino–
neutrino forward-scattering inside the dense anisotropic interior of the star and can
lead to fast collective neutrino oscillations. We present the fast ever theory of
fast flavor conversion beyond the linear regime to show how the different neutrino
flavors are brought closer to each other, or in other words, flavor depolarizes due
to irreversible decoherence-like processes occurring at a Tera-Hz rate, determined
by the large neutrino density. Our theory explains how depolarization happens, when
does it happen, what determines the epoch and finally describes a method to calculate
the extent of depolarized fluxes. This new result allows detailed implementation of
flavor-dependent neutrino transport in supernova simulations and paves the way for
supernova neutrino phenomenology.