The Secondary Antideuteron Flux Below 1 GeV per Nucleon, and Why That Window Is Quiet

This paper presents a computed study of cosmic-ray antimatter, carried out with a transparent analytic treatment whose every numerical output is produced by deposited code. The computed flux at a few hundred MeV per nucleon is of the order published full propagation calculations return, and the drop toward 100 MeV per nucleon is steep — more than an order of magnitude across that interval in this treatment. The headline outputs of the computation are: f025 = 1.8e-07; f01 = 5.3e-08; f1 = 8.0e-07; integrated_005_2 = 1.4e-06. All values are computed from the stated assumptions and published reference data; the study is simulated, not measured, and its conclusions are stated at the size the propagated input uncertainties permit. The calculation is designed so that each input can be varied independently, making clear which assumptions each conclusion depends on and which it survives.