Nonperturbative Anomalous Thresholds

09.05.2023 14:00 – 15:00

Abstract: Feynman diagrams (notably the triangle diagram) involving heavy enough particles contain branch cuts on the physical sheet—anomalous thresholds—which, unlike normal thresholds and bound-state poles, do not correspond to any asymptotic n-particle state. “Who ordered that?” I will show that anomalous thresholds arise as a consequence of established S-matrix principles and two reasonable assumptions: unitarity below the physical region and analyticity in the mass. I will derive explicit non-perturbative formulas for the discontinuity across the anomalous threshold in d=2, and in d=4, ready to be used in dispersion relations for bootstrap and phenomenological applications.

Lieu

Bâtiment: Ecole de Physique

Room 234

entrée libre