Flavor distribution of UHE cosmic neutrino oscillations at neutrino telescopes

If the ultrahigh-energy (UHE) cosmic neutrinos produced from a distant astrophysical source can be measured at a km3km3-size neutrino telescope such as the IceCube or KM3NeT, they will open a new window to understand the nature of flavor mixing and to probe possible new physics. Considering the conventional UHE cosmic neutrino source with the flavor ratio φe:φμ:φτ=1:2:0φe:φμ:φτ=1:2:0, I point out two sets of conditions for the flavor democracy φeT:φμT:φτT=1:1:1 to show up at neutrino telescopes: either θ13=0θ13=0 and θ23=π/4θ23=π/4 (CP invariance) or δ=±π/2δ=±π/2 and θ23=π/4θ23=π/4 (CP violation) in the standard parametrization of the 3×33×3 neutrino mixing matrix V  . Allowing for slight μμ–ττ symmetry breaking effects characterized by Δ∈[-0.1,+0.1]Δ∈[-0.1,+0.1], I find φeT:φμT:φτT=(1-2Δ):(1+Δ):(1+Δ) as a good approximation. Another possibility to constrain ΔΔ is to detect the ν¯e flux of Eν¯e≈6.3PeV via the Glashow resonance channel ν¯ee→W-→anything. I also give some brief comments on (1) possible non-unitarity of V in the seesaw framework and its effects on the flavor distribution at neutrino telescopes and (2) a generic description and determination of the cosmic neutrino flavor composition at distant astrophysical sources.