The Effect of the Collisional Flavor Instability on Core-Collapse Supernova Models

TL;DR

This study investigates the impact of the neutrino collisional flavor instability on core-collapse supernova models, finding that its effects are minimal due to slow growth rates and stochastic turbulence.

Contribution

The paper provides a detailed comparison of growth rates of collisional flavor instability modes using multi-group and monochromatic approximations, highlighting the limited influence on supernova dynamics.

Findings

Monochromatic approximation overestimates growth rates.

Actual growth rates are at most ~200 s$^{-1}$, too slow to affect outcomes.

Flavor conversion effects are weak and overshadowed by turbulence.

Abstract

We explore the effects of the neutrino collisional flavor instability (CFI) based on 1D and 2D core-collapse supernova (CCSN) simulations done using the sophisticated radiation-hydrodynamic code Fornax. We compare the growth rates of homogeneous CFI (hCFI) modes calculated by numerically solving the multi-group dispersion relation to those calculated using the monochromatic approximation. We find that the widely-used monochromatic approximation leads to incorrect growth rates} when applied in multi-group scenarios. As opposed to the $\sim10^5$ s$^{-1}$ values given by the monochromatic approximation, the actual growth rates of non-resonance multi-group hCFI are at most $\sim$200 s$^{-1}$ in all our models and they are too slow to affect CCSN outcomes. We adopt a BGK flavor conversion scheme in the simulations to include the effects of resonance-like hCFI. We find that the CCSN dynamics and neutrino emission properties are only weakly influenced, and the intrinsic stochasticity due to convection and neutrino-driven turbulence can naturally lead to comparable effects. Hence, our analysis of the non-resonance and resonance-like hCFI into CCSN simulations suggests that the effects of neutrino flavor conversion triggered by hCFI modes are in general small.