Flavor distribution of UHE cosmic neutrino oscillations at neutrino telescopes

摘要

If the ultrahigh-energy (UHE) cosmic neutrinos produced from a distant astrophysical source can be measured at a km~3-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 φ_e : φ_μ :φ_τ = 1 : 2 : 0, I point out two sets of conditions for the flavor democracy φ_e~T:φ_μ~T: φ_τ~T = 1 : 1 : 1 to show up at neutrino telescopes: either θ_(13) = 0 and θ_(23) = π/4 (CP invariance) or δ = ±π/2 and θ_(23) = n/4 (CP violation) in the standard parametrization of the 3 × 3 neutrino mixing matrix V. Allowing for slight μ-τ symmetry breaking effects characterized by Δ∈ -0.1, +0.1, I find φ_e~T : φ_μ~T : φ_τ~T = (1 — 2Δ) : (1 + Δ) : (1 + Δ) as a good approximation. Another possibility to constrain Δ is to detect the v_e flux of E_(v_e)≈ 6.3 PeV via the Glashow resonance channel v_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.