# Distinguishing Dirac and Majorana neutrinos by their gravi-majoron decays

## TL;DR

This paper proposes a method to distinguish Dirac and Majorana neutrinos by analyzing their decay signatures involving gravi-majorons, using astrophysical neutrino spectra and experimental bounds on neutrino lifetimes.

## Contribution

It introduces a novel approach to differentiate neutrino types through decay channels involving gravi-majorons and derives bounds on neutrino lifetimes from experimental data.

## Key findings

- Bounds on neutrino lifetimes for Majorana case: τ2/m2 > 1.1×10^{-3} s/eV and τ3/m3 > 2.2×10^{-5} s/eV.
- Decay signatures differ for Dirac and Majorana neutrinos in astrophysical observations.
- Potential to identify neutrino nature using high-energy astrophysical neutrino spectra.

## Abstract

Neutrinos may acquire small Dirac or Majorana masses by new low-energy physics in terms of the chiral gravitational anomaly, as proposed by Dvali and Funcke (2016). This model predicts fast neutrino decays, $\nu_i\to\nu_j+\phi$ and $\nu_i\to\bar{\nu}_j+\phi$, where the gravi-majorons $\phi$ are pseudoscalar Nambu-Goldstone bosons. The final-state neutrino and antineutrino distributions differ depending on the Dirac or Majorana mass of the initial state. This opens a channel for distinguishing these cases, for example in the spectrum of high-energy astrophysical neutrinos. In particular, we put bounds on the neutrino lifetimes in the Majorana case, ${\tau_2}/{m_2}> 1.1\times 10^{-3}(6.7\times 10^{-4})~{\rm s/eV}$ and ${\tau_3}/{m_3}> 2.2\times 10^{-5}(1.3\times 10^{-4})~{\rm s/eV}$ at 90% CL for hierarchical (degenerate) masses, using data from experiments searching for antineutrino appearance from the Sun.