Rethinking Partial Widths: Unitary Mixing and the $Δ(1232)$ Pole Residue

Abstract

The extracted $πN$ partial decay width of the $Δ(1232)$ systematically exceeds its total width ($2|r|>Γ$). We demonstrate this anomaly is a natural consequence of S-matrix unitary mixing. Because exact multi-channel shadow poles are distant and model-dependent, we utilize a heuristic elastic model -- treating the overlapping $Δ(1600)$ as fully elastic -- to isolate the core mechanism. We show that evaluating a perturbing S-matrix at a state's complex pole systematically inflates the residue magnitude. This proof of principle confirms complex residues reflect global amplitude topology rather than isolated intrinsic properties, challenging naive interpretations of branching fractions.