Frequency Drift in Repeating Bursts as a Dispersion-Slope Test

This paper evaluates the dispersion error that would be required to mimic the downward frequency drift observed in repeating fast radio bursts, using the differentiated cold-plasma delay law, and derives the drift's frequency scaling and band-crossing scales to separate dedispersion artefacts from genuine source and lensing physics. The headline results are as follows. Dispersion error that would mimic a drift of minus 20 MHz per ms at 600 MHz: 1.3 pc cm-3; Delay slope across the 400 MHz band from a dispersion error of one unit at 600 MHz: 15.4 ms; Drift rate at 1.4 GHz if the drift scales linearly with frequency from 600 MHz: -46.7 MHz per ms; Time for a drifting sub-burst to cross the 400 MHz band at the stated rate: 20 ms; Frequency drift produced in one millisecond by a plasma lens moving at the stated scaling (illustrative one percent path change): 6 MHz; Residual dispersion precision of modern repeater timing compared with the mimicking error: 130. All values are computed from the stated assumptions and published inputs; the study is simulated and computed, not measured.