2022-03-11 11:00 Online
Theory of Fast flavor conversion of Supernova neutrinos
Soumya Bhattacharyya
(Seminar Cancelled)
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 neutrino flavors to oscillate collectively at a very fast rate known as "Fast Flavor Conversion". Although the triggering and initial growth of fast conversions are understood, owing to its complicated nonlinear evolution, the final impact is not yet known. Interestingly, stellar explosion and the neutrino signal are sensitive to the processed flavor-dependent fluxes, but the required neutrino theory prediction is still lacking. Moreover, the fact that the different neutrino flavors have hierarchical interaction rates can produce relative forward excesses in the fluxes of νx over anti-νe, and anti-νe over νe in the decoupling region of a supernova which can develop a zero crossing in phase space for the neutrino angular distributions and act as a criterion for the fast instability to occur. In the first half of my talk I will address this crucial theoretical or phenomenological obstacle and 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 it happens, what determines the epoch and finally describes a method to calculate the extent of depolarized neutrino fluxes. In the second half of my talk I will present a linearized analysis to explain the dependence of fast oscillations on the nature of the neutrino angular distributions, especially its symmetry property, the number of zero crossings, lepton asymmetry etc. All these new results can play a crucial role for future supernova theory and neutrino phenomenology.