Current neutrino oscillation data indicate that θ 13 is not strongly suppressed and θ 23 might have an appreciable deviation from π / 4 , implying that the 3 × 3 neutrino mixing matrix V does not have an exact μ – τ permutation symmetry. We make a further study of the effect of μ – τ symmetry breaking on the democratic flavor distribution of ultrahigh-energy (UHE) cosmic neutrinos at a neutrino telescope, and find that it is characterized by | V μ i | 2 ? | V τ i | 2 which would vanish if either θ 23 = π / 4 and θ 13 = 0 or θ 23 = π / 4 and δ = ± π / 2 held. We observe that the second-order μ – τ symmetry breaking term Δ ˉ may be numerically comparable with or even larger than the first-order term Δ in the flux ratios ? e T : ? μ T : ? τ T ? ( 1 ? 2 Δ ) : ( 1 + Δ + Δ ˉ ) : ( 1 + Δ ? Δ ˉ ) , if sin ( θ 23 ? π / 4 ) and cos δ have the same sign. The detection of the UHE ν ˉ e flux via the Glashow-resonance channel ν ˉ e e → W ? → anything is also discussed by taking account of the first- and second-order μ – τ symmetry breaking effects.
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