Resonant Spin-Flavor Conversion of Supernova Neutrinos: Dependence on Electron Mole Fraction

TL;DR

This paper investigates how the electron mole fraction in supernova environments influences resonant spin-flavor neutrino conversions, affecting observable neutrino spectra and event ratios, which can reveal neutrino properties and supernova conditions.

Contribution

It provides a detailed analysis of the dependence of RSF neutrino conversion on electron mole fraction and explores observable signatures in supernova neutrino detection.

Findings

Flavor conversion depends on Ye and mass hierarchy.

Event ratio variations can indicate RSF effects.

Time-dependent signatures help probe supernova conditions.

Abstract

Detailed dependence of resonant spin-flavor (RSF) conversion of supernova neutrinos on electron mole fraction Ye is investigated. Supernova explosion forms a hot-bubble and neutrino-driven wind region of which electron mole fraction exceeds 0.5 in several seconds after the core collapse. When a higher resonance of the RSF conversion is located in the innermost region, flavor change of the neutrinos strongly depends on the sign of 1-2Ye. At an adiabatic high RSF resonance the flavor conversion of bar{nu}_e -> nu_{mu,tau} occurs in Ye < 0.5 and normal mass hierarchy or in Ye > 0.5 and inverted mass hierarchy. In other cases of Ye values and mass hierarchies, the conversion of nu_e -> bar{nu}_{mu,tau} occurs. The final bar{nu}_e spectrum is evaluated in the cases of Ye < 0.5 and Ye > 0.5 taking account of the RSF conversion. Based on the obtained result, time variation of the event number ratios of low bar{nu}_e energy to high bar{nu}_e energy is discussed. In normal mass hierarchy, an enhancement of the event ratio should be seen in the period when the electron fraction in the innermost region exceeds 0.5. In inverted mass hierarchy, on the other hand, a dip of the event ratio should be observed. Therefore, the time variation of the event number ratio is useful to investigate the effect of the RSF conversion.