Time of Flight and Supernova Progenitor Effects on the Neutrino Halo

TL;DR

This paper investigates how the neutrino halo in supernovae is affected by the timing of neutrino emission, revealing that accounting for time of flight is crucial for understanding flavor conversions and that early times may allow neglecting the halo.

Contribution

It demonstrates that the common constant time approximation is insufficient and introduces the importance of time of flight corrections in modeling the neutrino halo in supernovae.

Findings

Time of flight corrections can trigger fast neutrino flavor conversion.

Early supernova phases have negligible neutrino halo effects.

Neglecting the halo may be valid at early times.

Abstract

We argue that the neutrino halo, a population of neutrinos that have undergone direction-changing scattering in the stellar envelope of a core-collapse supernova (CCSNe), is sensitive to neutrino emission history through time of flight. We show that the constant time approximation, commonly used in calculating the neutrino halo, does not capture the spatiotemporal evolution of the halo neutrino population and that correcting for time of flight can produce conditions which may trigger fast neutrino flavor conversion. We also find that there exists a window of time early in all CCSNe where the neutrino halo population is sufficiently small that it may be negligible. This suggests that collective neutrino oscillation calculations which neglect the Halo may be well founded at sufficiently early times.