Abstract
We study cosmological scenarios in which high-energy neutrinos are emitted from the decay of long-lived massive particles at the cosmic time later than a redshift of 10^6. The high-energy neutrino events recently observed by the IceCube experiment suggest a new source of high-energy cosmic-ray neutrinos; decay of a heavy particle can be one of the possibilities. We calculate the spectrum of the high-energy neutrinos emitted from the decay of long-lived particles, taking account of the neutrino scattering processes with background neutrinos. Then, we derive bounds on the scenario using the observation of high-energy cosmic-ray neutrino flux. We also study constraints from the spectral distortions of the cosmic microwave background and the big-bang nucleosynthesis. In addition, we show that the PeV neutrinos observed by the IceCube experiment can originate from the decay of a massive particle with its mass as large as O(10^10 GeV).
Highlights
JHEP10(2014)150 scenario “early-decay scenario,” in contrast to the ones with decaying dark matter
Photons and charged particles are produced in association with the neutrino scattering processes; they result in the spectral distortion of the cosmic microwave background (CMB) and the change of the light-element abundances produced by the big-bang nucleosynthesis (BBN), from which we obtain an upper bound on the abundance of X
For the study of the constraints from the CMB distortion, we take into account the present bound (COBE/FIRAS [13, 14]), or the expected bound in the future
Summary
Let us first discuss the evolution of the neutrino flux produced by the decay of the parent particle X. A sizable amount of high-energy photons may be produced as a consequence of neutrinoneutrino scattering processes (after the hadronization and/or decay of colored particles). We approximate that the doublephoton pair productions of the fermions other than e± become ineffective for the photon with the energy E once the ratio of the scattering rates Γγγ→μ+μ−/Γγγ→e+e− becomes smaller than m2e/ET (with me being the electron mass); here, we use the fact that Ei−Ef ∼ O(m2e/T ), where Ei and Ef are energies of energetic initial- and final-state particles in the processes γγ → e+e− and e±γ → e±γ. This is due to the fact that the neutrinos with lower present energies are more likely to be affected by the scattering processes with the background neutrinos because they are produced at higher redshifts.
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