Distinguishing Dirac and Majorana Neutrinos: Resonant Spin-Flavor Precession of GeV-Scale Astrophysical Transients

Abstract

We present a unified formalism to study the Resonant Spin-Flavor Precession (RSFP) of high-energy ($\sim 1$ GeV) transient astrophysical neutrinos as a probe of their fundamental Dirac or Majorana nature. Current MeV scale neutrino studies face stringent restrictions: efficient core RSFP for Dirac supernova neutrinos is excluded by SN1987A cooling bounds, while solar neutrino conversion is tightly constrained by Borexino data. We show that considering the 1 GeV energy scale accessible through solar flares modifies the resonance conditions. For 1 GeV solar flare neutrinos, the resonance shifts to the tachocline and convective zones, where toroidal magnetic fields ($B \sim 50$ kG) induce adiabatic spin flavor conversion. In contrast, for supernovae, to avoid the cooling constraints, the RSFP is moved from the core supernovae to the stellar envelope. As for non thermal 1 GeV supernova neutrinos, the resonance is located in the dilute stellar wind where magnetic fields are negligible, suppressing RSFP and preserving the flux, one can use these non-thermal neutrinos as a candle to calibrate our signal, reducing its dependence on astrophysical uncertainties. Evaluating these helicity transitions through a density matrix approach, we predict distinct asymmetries in Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS) and neutrino-electron scattering cross-sections for solar flare neutrinos and supernova neutrinos. Our proposal provides a viable method to distinguish Dirac from Majorana neutrinos and to probe magnetic moments down to $\mu_\nu \sim 10^{-14} \mu_B$.