Paper detail

Distinguishing Dirac and Majorana neutrinos by their gravi-majoron decays

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, $ν_i\toν_j+ϕ$ and $ν_i\to\barν_j+ϕ$, where the gravi-majorons $ϕ$ 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, ${τ_2}/{m_2}> 1.1\times 10^{-3}(6.7\times 10^{-4})~{\rm s/eV}$ and ${τ_3}/{m_3}> 2.2\times 10^{-5}(1.3\times 10^{-4})~{\rm s/eV}$ at 90% CL for hierarchical (degenerate) masses, using data from experiments searching for antineutrino appearance from the Sun.