  We consider long-lived relic particles as the source of the PeV-scale
neutrinos detected at the IceCube observatory over the last six years. We
derive the present day neutrino flux, including primary neutrinos from direct
decays, secondary neutrinos from electroweak showering, and tertiary neutrinos
from re-scatters off the relic neutrino background. We compare the high-energy
neutrino flux prediction to the most recently available datasets and find
qualitative differences to expected spectra from other astrophysical processes.
We utilize electroweak corrections to constrain heavy decaying relic
abundances, using measurements impacted by electromagnetic energy injection,
such as light element abundances during Big Bang nucleosynthesis, cosmic
microwave background anisotropies, and diffuse $\gamma$-ray spectra. We compare
these abundances to those necessary to source the IceCube neutrinos and find
two viable regions in parameter space, ultimately testable by future neutrino,
$\gamma$-ray, and cosmic microwave background observatories.
