Abstract
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 γ-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, γ-ray, and cosmic microwave background observatories.
Highlights
Been considered in the past [10,11,12,13,14,15,16,17,18]
We explore how the decaying relic model is constrained by its impact on light element abundances, CMB anisotropies, and diffuse γ-ray spectra, after including the EW shower effects
This leads to the production of roughly the same amount of neutral and charged leptons for center-of-mass (COM) energies far beyond the EW scale. This is a side effect of unbroken isospin in the high-energy limit. This implies that any high-energy neutrino spectrum sourced directly from a heavy relic decay will be accompanied by a spectrum of electromagnetically interacting particles, which will carry roughly the same amount of energy as the neutrino spectrum
Summary
We consider two models in which our relic, X, directly decays to neutrinos. At ultra-high energies, the final state radiation includes many soft W ’s, which turn charged leptons into neutral ones and vice versa This leads to the production of roughly the same amount of neutral and charged leptons for center-of-mass (COM) energies far beyond the EW scale. This is a side effect of unbroken isospin in the high-energy limit. The qualitative features of the EW jets are model independent, as any heavy particle that decays to neutrinos will radiate gauge bosons. To zeroth order, this effect takes a delta function centered around. Model-dependent constraints on these production mechanisms exist based on measurements such as isocurvature; these are not stringent enough to rule out the small abundance of decaying relics necessary to source the IceCube neutrinos [42, 43]
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