Expected flavor composition of supernova neutrinos

TL;DR

This paper predicts the flavor composition of supernova neutrinos at Earth, showing that matter effects and decoherence lead to robust, order-dependent flavor ratios, with near equipartition in inverted hierarchy.

Contribution

It provides a model-independent prediction of supernova neutrino flavor ratios based on decoherence and standard matter effects, applicable across different supernova dynamics.

Findings

For normal hierarchy, electron-flavor fraction is less than 0.5.

For inverted hierarchy, flavor ratios are near 1/3, indicating equipartition.

Shock waves drive flavor ratios toward equipartition in normal hierarchy.

Abstract

We revisit the flavor composition of neutrinos from core-collapse supernovae (SN), focusing on robust predictions that are insensitive to the poorly known dynamics of collective flavor conversion in the inner core. Assuming that the many different trajectories and microscopic histories of neutrinos lead to decoherence of the ensemble at the boundary between the region of collective effects and the Mikheyev-Smirnov-Wolfenstein (MSW) dominated layers, we show that standard matter effects alone strongly constrain the electron-flavor fraction at Earth. For normal mass ordering (NO) we obtain $f_{\nu_e}^{\rm NO}\lesssim 0.5$ at all times and energies, while for inverted ordering (IO), we predict $f_{\nu_e}^{\rm IO}\simeq 1/3$, i.e.\ near flavor equipartition. Shock-wave propagation through the high (H) MSW resonance drives the system toward equipartition also in NO. In this way our framework links simple assumptions about decoherence and standard matter effects to robust expectations for the flavor evolution inside core-collapse supernovae. This contribution summarizes the main results of arXiv:2403.14762.