How did IceCube detect high-energy astrophysical neutrinos and what alternative explanations exist for its events?

Lens adapted to this topic: Competing source and background explanations

Serious alternatives do not generally dispute that IceCube recorded unusual high-energy events; they question how much is atmospheric, cosmogenic, or attributable to particular classes of cosmic sources. Analyses find conventional atmospheric and cosmogenic explanations strongly disfavored for the earliest PeV cascades, while prompt atmospheric and diffuse astrophysical components remain quantitative possibilities. The lack of identified point sources leaves source composition open.

• For the earliest PeV cascade events, conventional atmospheric and cosmogenic neutrinos were found to be strongly disfavored, but prompt atmospheric neutrinos and diffuse astrophysical backgrounds remained possible explanations requiring further analysis.
• Cosmogenic neutrinos arise when ultra-high-energy cosmic rays interact with ambient photon backgrounds; IceCube searches use them to constrain cosmic-ray sources and models.
• A two-component power-law model can fit the four-year starting-event data slightly better than a single power law, although the cited analysis says the improvement is not decisive.
• The tested diffuse-flux models were not substantially preferred over a single power law, leaving the population mix and spectrum incompletely determined.
• The absence of IceCube neutrinos above 10 PeV has been used to examine tensions with expectations for extremely high-energy events and to constrain possible cosmic-ray-source populations.

Featured source[1306.2309] Demystifying the PeV Cascades in IceCube: Less (Energy) is More (Events)ar5iv.labs.arxiv.org6 sourcesView sources