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Neutrino Flavor and Spin Transformations in Astrophysical Environments


We discuss and explore the neutrino spin and flavor evolution of neutronization burst neutrinos inside an Oxygen-Neon-Magnesium (ONeMg) type IIa supernova. In addition, we look at the flavor evolution of neutrinos originating from the disk-like (temporary) remnant of a binary neutron star (BNS) merger environment. Computer simulations were run to simulate coherent, forward (non direction changing) scattering of Majorana type neutrinos in these environments. We find in our simulations that, a large neutrino mass ($\approx 10eV$), a flat electron fraction profile, and a high neutrino luminosity are needed to produce a significant spin coherence effect. However, if such a spin transformation does occur (e.g. by other non-linear feedback mechanisms that we did not consider here), these spin transformations can have a significant, qualitative, effect on the subsequent flavor evolution of the neutrinos. In the case of the BNS merger environments, we found bipolar spectral swaps which are reminiscent of neutrino flavor evolution in the neutrino driven wind environments in supernovae. These flavor transformations can potentially increase the electron fraction and thereby weaken the $r$-process in these environments.

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