Oscillations of sterile neutrinos from dark matter decay eliminates the IceCube-Fermi tension

IceCube has observed a flux of cosmic neutrinos, with a “bump” in the energy range $10\lesssim E/\mathrm{TeV}\lesssim 100$ that creates a $3\sigma$ tension with $\gamma$-ray data from the Fermi satellite. This has been interpreted as evidence for a population of hidden cosmic-ray accelerators. We propose an alternative explanation of this conundrum on the basis of cold dark matter which decays into sterile neutrinos after oscillations produce the bump in the cosmic neutrino spectrum.

Figure 1

The lifetime ${\tau }_{\mathrm{dc}}$ versus $m_{\mathrm{dc}}$ for $E_{\mathrm{peak}}=1.37\times {10}^5\mathrm{GeV}$ (solid line), $8.36\times {10}^4\mathrm{GeV}$ (lower dashed line), and $1.87\times {10}^5\mathrm{GeV}$ (upper dashed line). The shaded purple regions are excluded based on the requirement that ${\chi }_{\mathrm{dc}}\to {\nu }_s{\overline{\nu }}_s$ decays contribute less than 1% of the peak of $E^2{\mathrm{\Phi }}_{(\nu +\overline{\nu }{)}_{\mathrm{SM}}}$, so the shaded red regions correspond to excluded values of $m_{\mathrm{dc}}$, accounting for the range of $E_{\mathrm{peak}}$. The cross marks the fiducial point of our analysis.

Figure 2

The quantity $E^2{\mathrm{\Phi }}_{(\nu +\overline{\nu }{)}_{\mathrm{SM}}}$ as a function of $E/ϵ$ assuming $E_{\mathrm{peak}}=1.37\times {10}^5\mathrm{GeV}$ and the decay of ${\chi }_{\mathrm{dc}}$ to sterile neutrinos contributes $\max (E^2{\mathrm{\Phi }}_{(\nu +\overline{\nu }{)}_{\mathrm{SM}}})=5.80\times {10}^{-8}\mathrm{GeV}/({\mathrm{cm}}^2\mathrm{s}\mathrm{sr})$.

Figure 3

The total extragalactic $\gamma$-ray background (open symbols) reported by the Fermi Collaboration [6] and the diffuse astrophysical flux (solid symbols) reported by the IceCube Collaboration (frequentist statistical analysis 7.5 yr data) [3]. The $\gamma$-ray result is shown for three foreground models, with the yellow band showing background modeling uncertainties and the gray band showing the cumulative intensity from resolved Fermi sources at latitudes $|b|>20°$. The SM diffuse astrophysical neutrino flux is shown with the horizontal dashed line, and the SM neutrino flux from dark matter decays is shown with the magenta dashed line.