Cosmogenic Neutrino Fluxes and the Cost of Removing High-Redshift Sources

Cosmogenic neutrinos, produced when ultra-high-energy cosmic rays strike the cosmic microwave background, are the one guaranteed flux whose sources lie preferentially at high redshift. This paper computes how strongly the flux depends on source evolution and what a high-redshift truncation costs it. The evolution factor grows from 0.887 for non-evolving sources to 8.66 for evolution as (1+z)^3 and 60.4 for (1+z)^5. Calibrating the strong-evolution case to a peak E-squared flux of 1.000e-08 at 10^18 eV, the non-evolving case predicts only 1.024e-09. Truncating the source history at redshift 2 — an effective stand-in for histories in which the early universe offers far less time at high temperature — multiplies the strong-evolution flux by 0.496, giving 4.964e-09. Unlike the TeV-PeV diffuse flux, whose weighting is local, the cosmogenic flux genuinely samples the early universe, and its future detection or tighter exclusion will grade source histories — including truncated ones — directly. The study is computed from stated assumptions, not measured.