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.
Highlights
A completely new approach to explain small Dirac or Majorana neutrino masses [1] relies on new physics at the low-energy frontier of particle physics instead of highenergy extensions of the Standard Model
Neutrino decays imply a distinct flavor composition of long-traveling astrophysical neutrinos because all neutrinos arrive in the lightest mass state
Interactions between neutrinos and conventional Nambu-Goldston bosons are strongly constrained by cosmology, astrophysics, and laboratory experiments
Summary
A completely new approach to explain small Dirac or Majorana neutrino masses [1] relies on new physics at the low-energy frontier of particle physics instead of highenergy extensions of the Standard Model. In the current paper we predict that the low-energy gravitational mass model offers an additional opportunity through fast νi → ð−νÞj þ φ decays. We argue that the νi → ν j þ φ decays in the gravitational mass model are in principle fast enough to distinguish between the Majorana and Dirac cases by using the flux and spectrum of the daughter neutrinos. Majorana neutrinos would decay to antineutrinos, whereas Dirac neutrinos would decay to sterile states While these methods are not yet experimentally feasible, with the current data we can put strong bounds on the Majorana case using null results from experiments searching for antineutrino appearance from the Sun. The paper is structured as follows.
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