Evolution and the quasistationary state of collective fast neutrino flavor conversion in three dimensions without axisymmetry

TL;DR

This study explores the evolution of fast neutrino flavor conversion in three dimensions without axisymmetry, revealing a quasistationary state with specific angular distribution properties and proposing generalized analytical models.

Contribution

It extends previous 1D models to 3D, demonstrating the system's evolution to a quasistationary state and developing new analytical prescriptions for predicting flavor conversion outcomes.

Findings

System reaches a quasistationary state with no ELN crossings.

Near flavor equilibration occurs in one angular domain.

Analytical models show promising predictions for post-FFC moments.

Abstract

We investigate in this work the evolution of the collective fast neutrino flavor conversion (FFC) in a three dimensional (3D) cubic box with periodic boundary condition for three different neutrino angular distributions that are axially asymmetric. We find that the system evolves toward a quasistationary state where the angular distribution of the spatially averaged neutrino electron-minus-muon lepton number (ELN) does not contain any crossings. In the quasistationary state, near flavor equilibration is achieved in one angular domain enclosed by the initial ELN angular crossing contour, similar to the conclusion derived based on simplified one dimensional (1D) system with axially symmetric neutrino angular distributions. We have also performed additional simulations in coordinates where the initial first ELN angular moment has only one nonvanishing spatial component by using the original axially asymmetric ELN angular distributions as well as the corresponding axisymmetric ELN distributions, and find interesting similarity between these two sets. Finally, we propose three different analytical prescriptions generalized from earlier 1D models to 3D models, and evaluate their performances in predicting the post-FFC moments. Our findings suggest that further development of effective classical transport model in multidimensions to capture the effect of FFC is promising.