IceCube neutrinos, decaying dark matter, and the Hubble constant

Abstract

Cosmological parameters deduced from the Planck measurements of anisotropies in the cosmic microwave background are at some tension with direct astronomical measurements of various parameters at low redshifts. Very recently, it has been conjectured that this discrepancy can be reconciled if a certain fraction of dark matter is unstable and decays between recombination and the present epoch. Herein we show that if the superheavy relics have a branching into neutrinos B (X \to ν\bar ν) \sim 3 \times 10^{-9}, then this scenario can also accommodate the recently discovered extraterrestrial flux of neutrinos, relaxing the tension between IceCube results and Fermi LAT data. The model is fully predictive and can be confronted with future IceCube data. We demonstrate that in 10 years of observation IceCube will be able to distinguish the mono-energetic signal from X decay at the 3σlevel. In a few years of data taking with the upgraded IceCube-Gen2 enough statistics will be gathered to elucidate the dark matter--neutrino connection at the 5σlevel.

Figures (1)

• Figure 1: The open symbols represent the total extragalactic $\gamma$-ray background for different foreground (FG) models as reported by the Fermi LAT Collaboration Ackermann:2014usa. For details on the modeling of the diffuse Galactic foreground emission in the benchmark FG models A, B and C, see Ackermann:2014usa. The cumulative intensity from resolved Fermi LAT sources at latitudes $|b| > 20^\circ$ is indicated by a (grey) band. The solid symbols indicate the neutrino flux (per flavor) reported by the IceCube Collaboration. The blue points are from the data sample of the most recent IceCube analysis Aartsen:2014muf. The light grey data points are from the 3-year data sample of Aartsen:2013bka, shifted slightly to the right for better visibility. The best fit to the data (extrapolated down to lower energies), is also shown for comparison Aartsen:2014muf. The dashed line indicates the mono-energetic signal from dark matter decay. Note that a plotting of $E^2 \Phi = E dF/(d\Omega \, dA \, dt \, d \ln E )$ versus $\ln E$ conserves the area under a spectrum even after processing the electromagnetic cascade. Thus, the area of the $\pi^0$ contribution to the diffuse $\gamma$-ray spectrum (total diffuse $\gamma$-ray flux provides an upper bound) implies the low energy cutoff (upper bound) to the $\pi^\pm$ origin of the neutrinos.