Distinguishing Dirac and Majorana neutrinos by their gravi-majoron decays

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, ${\nu }_i\to {\nu }_j+\varphi$ and ${\nu }_i\to {\bar{\nu }}_j+\varphi$, where the gravi-majorons $\varphi$ 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, ${\tau }_2/m_2>1.1\times 10^{-3}(6.7\times 10^{-4})s/eV$ and ${\tau }_3/m_3>2.2\times 10^{-5}(1.3\times 10^{-4})s/eV$ at 90% CL for hierarchical (degenerate) masses, using data from experiments searching for antineutrino appearance from the Sun.

12 pages, 1 figure, matches the version published in PRD with the title "Distinguishing Dirac and Majorana neutrinos by their decays via Nambu-Goldstone bosons in the gravitational-anomaly model of neutrino masses"