This paper presents the results from point-like neutrino source searches using ten years of IceCube data collected between Apr. 6, 2008 and Jul. 10, 2018. We evaluate the significance of an astrophysical signal from a point-like source looking for an excess of clustered neutrino events with energies

We report a quasidifferential upper limit on the extremely-high-energy (EHE) neutrino flux above 5 × 10 6 GeV based on an analysis of nine years of IceCube data. The astrophysical neutrino flux measured by IceCube extends to PeV energies, and it is a background flux when searching for an independent signal flux at higher energies, such as the cosmogenic neutrino signal. We have developed a new method to place robust limits on the EHE neutrino flux in the presence of an astrophysical background, whose spectrum has yet to be understood with high precision at PeV energies. A distinct event with a deposited energy above 10 6 GeV was found in the new two-year sample, in addition to the one event previously found in the sevenyear EHE neutrino search. These two events represent a neutrino flux that is incompatible with predictions for a cosmogenic neutrino flux and are considered to be an astrophysical background in the current study. The obtained limit is the most stringent to date in the energy range between 5 × 10 6 and 2 × 10 10 GeV. This result constrains neutrino models predicting a three-flavor neutrino flux of E 2 ν ϕ ν e þν μ þν τ ≃ 2 × 10 −8 GeV=cm 2 sec sr at 10 9 GeV. A significant part of the parameter space for EHE neutrino production scenarios assuming a proton-dominated composition of ultra-high-energy cosmic rays is disfavored independently of uncertain models of the extragalactic background light which previous IceCube constraints partially relied on.

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With the observation of high-energy astrophysical neutrinos by the IceCube Neutrino Observatory, interest has risen in models of PeV-mass decaying dark matter particles to explain the observed flux. We present two dedicated experimental analyses to test this hypothesis. One analysis uses 6 years of IceCube data focusing on muon neutrino ‘track’ events from the Northern Hemisphere, while the second analysis uses 2 years of ‘cascade’ events from the full sky. Known background components and the hypothetical flux from unstable dark matter are fitted to the experimental data. Since no significant excess is observed in either analysis, lower limits on the lifetime of dark matter particles are derived: we obtain the strongest constraint to date, excluding lifetimes shorter than at 90% CL for dark matter masses above .