Simulating nonlinear neutrino flavor evolution

TL;DR

This paper introduces numerical methods to simulate the complex, nonlinear flavor evolution of neutrinos in supernovae, revealing phenomena that could help determine neutrino properties like mass hierarchy and mixing angles.

Contribution

It presents two new computational codes for accurately modeling nonlinear neutrino flavor evolution in supernovae, uncovering unexpected flavor transformation phenomena.

Findings

Nonlinear effects significantly alter neutrino flavor evolution.

Potential detection signatures could reveal neutrino mass hierarchy.

New phenomena occur even with small neutrino mass differences.

Abstract

We discuss a new kind of astrophysical transport problem: the coherent evolution of neutrino flavor in core collapse supernovae. Solution of this problem requires a numerical approach which can simulate accurately the quantum mechanical coupling of intersecting neutrino trajectories and the associated nonlinearity which characterizes neutrino flavor conversion. We describe here the two codes developed to attack this problem. We also describe the surprising phenomena revealed by these numerical calculations. Chief among these is that the nonlinearities in the problem can engineer neutrino flavor transformation which is dramatically different than in standard Mikheyev-Smirnov-Wolfenstein treatments. This happens even though the neutrino mass-squared differences are measured to be small, and even when neutrino self-coupling is sub-dominant. Our numerical work has revealed potential signatures which, if detected in the neutrino burst from a Galactic core collapse event, could reveal heretofore unmeasurable properties of the neutrinos, such as the mass hierarchy and vacuum mixing angle theta_13.