On the flavor composition of the high-energy neutrinos in IceCube

AbstractThe IceCube experiment has recently released 3 years of data of the first ever detected high-energy (≳30TeV) neutrinos, which are consistent with an extraterrestrial origin. In this talk, we compute the compatibility of the observed track-to-shower ratio with possible combinations of neutrino flavors with relative proportion (αe:αμ:ατ)⊕. Although this observation is naively favored for the canonical (1 : 1 : 1)⊕ at Earth, once we consider the IceCube expectations for the atmospheric muon and neutrino backgrounds, this flavor combination presents some tension with data. We find that, for an astrophysical neutrino Eν−2 energy spectrum, (1 : 1 : 1)⊕ at Earth is currently disfavored at 92% C.L. We discuss the trend of this result by comparing the results with the 2-year and 3-year data. We obtain the best-fit for (1 : 0 : 0)⊕ at Earth, which cannot be achieved from any flavor ratio at sources with averaged oscillations during propagation. Although it is not statistically significant at present, if confirmed, this result would suggest either a misunderstanding of the expected background events, or a misidentification of tracks as showers, or even more compellingly, some exotic physics which deviates from the standard scenario