Neutrino Fast Flavor Instability in three dimensions for a Neutron Star Merger

TL;DR

This paper introduces a moment-based method to simulate fast neutrino flavor transformations in three dimensions during neutron star mergers, capturing key phases and length scales of the instability.

Contribution

The paper presents a novel angular moment method for modeling neutrino flavor evolution in complex astrophysical environments, improving computational efficiency and accuracy.

Findings

Successfully simulates fast flavor neutrino transformation in neutron star mergers

Captures growth, saturation, and decoherence phases of flavor instability

Accurately predicts the lengthscale of fastest-growing fluctuations

Abstract

The flavor evolution of neutrinos in core collapse supernovae and neutron star mergers is a critically important unsolved problem in astrophysics. Following the electron flavor evolution of the neutrino system is essential for calculating the thermodynamics of compact objects as well as the chemical elements they produce. Accurately accounting for flavor transformation in these environments is challenging for a number of reasons, including the large number of neutrinos involved, the small spatial scale of the oscillation, and the nonlinearity of the system. We take a step in addressing these issues by presenting a method which describes the neutrino fields in terms of angular moments. We apply our moment method to neutron star merger conditions and show it simulates fast flavor neutrino transformation in a region where this phenomenon is expected to occur. By comparing with particle-in-cell calculations we show that the moment method is able to capture the three phases of growth, saturation, and decoherence, and correctly predicts the lengthscale of the fastest growing fluctuations in the neutrino field.