2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/180655This article reviews a recently-discovered link between integrable quantum field theories and certain ordinary differential equations in the complex domain. Along the way, aspects of PT-symmetric quantum mechanics are discussed, and some elementary features of the six-vertex model and the Bethe ansatz are explained.102 pages, 27 figures. v2: added referencesHigh Energy Physics - Theorytext