Diffuse Neutrino Flux Redshift Weighting and the Effect of a High-Redshift Source Cutoff

The diffuse astrophysical neutrino flux measured by IceCube is an integral over cosmic history, and what that integral implies about source evolution depends on how the integrand is weighted with redshift. This paper computes the redshift weighting explicitly for a star-formation-like source evolution and asks a pointed question: if the source population had an earliest epoch, represented here by a cutoff at redshift 8 of the kind a bounced thermal history would impose, how much of the observed flux would be missing? The answer is small. Half of the weighted flux originates below redshift 1.28, 36.9 per cent of the weight lies below redshift 1 and 69.8 per cent below redshift 2, and truncating the population at redshift 8 removes only 2.21 per cent of the normalisation, moving the half-flux redshift from 1.28 to 1.26. A high-redshift cutoff of this kind therefore cannot reconcile the differing spectral fits reported from different event selections, whose normalisations at 100 TeV differ by a factor 2.5 and whose extrapolated fluxes cross near the PeV scale, with a ratio of 0.643 at 1 PeV. The calculation is a computation from stated assumptions, not a measurement.