Searching For Superheavy Decaying Particles With Ultra-High-Energy Neutrino Observatories

TL;DR

This paper explores how ultra-high-energy neutrino observatories can detect decays of superheavy relic particles from the early universe, providing new constraints and enhancing sensitivity beyond gamma-ray observations.

Contribution

It introduces a method to use neutrino fluxes from superheavy particle decays to improve detection sensitivity and constraints on long-lived relics.

Findings

IceCube and Fermi set new constraints on superheavy relics.

Next-generation neutrino telescopes will greatly improve detection sensitivity.

Neutrino fluxes from electromagnetic cascades can relax gamma-ray constraints.

Abstract

If there exist unstable but long-lived relics of the early universe, their decays could produce detectable fluxes of gamma rays and neutrinos. In this paper, we point out that the decays of superheavy particles, $m_{\chi} \gtrsim 10^{10} \, \text{GeV}$,would produce an enhanced flux of ultra-high-energy neutrinos through the processes of muon and pion pair production in the resulting electromagnetic cascades. These processes transfer energy from electromagnetic decay products into neutrinos, relaxing the constraints that can be derived from gamma-ray observations, and increasing the sensitivity of high-energy neutrino telescopes to superheavy particle decays. Taking this into account, we derive new constraints on long-lived superheavy relics from the IceCube Neutrino Observatory, and from the Fermi Gamma-Ray Space Telescope. We find that IceCube-Gen2, and other next generation neutrino telescopes, will provide unprecedented sensitivity to the decays of superheavy dark matter particles and other long-lived relics.