Testing neutrino instability with active galactic nuclei

TL;DR

This paper proposes using high-energy neutrinos from active galactic nuclei to test neutrino instability and decay channels, providing more stringent bounds on neutrino coupling strengths than previous methods.

Contribution

It introduces a novel method to constrain neutrino decay via astrophysical neutrino flux measurements, surpassing existing experimental bounds.

Findings

Neutrino decay can be tested over cosmological distances.

Coupling strength bounds can reach down to $10^{-8} eV/m$.

Flux measurements of different neutrino flavors provide key insights.

Abstract

Active galactic nuclei and gamma ray bursts at cosmological distances are sources of high-energy electron and muon neutrinos and provide a unique test bench for neutrino instability. The typical lifetime-to-mass ratio one can reach there is $\tau/m\sim 500 Mpc/cE_{\nu}\sim 500$ s/eV. We study the rapid decay channel $\nu_i\to\nu_j+\phi$, where $\phi$ is a massless or very light scalar (possibly a Goldstone boson), and point out that one can test the coupling strength of $g_{ij}\nu_i\nu_j$ down to $g_{ij}\lsim 10^{-8} eV/m$ by measuring the relative fluxes of $\nu_{e}$, $\nu_{\mu}$ and $\nu_{\tau}$. This is orders of magnitude more stringent bound than what one can obtain in other phenomena, e.g. in neutrinoless double beta decay with scalar emission.