HEP Theory Journal Club

Nonperturbative Anomalous Thresholds

Miguel Correia

McGill

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?” In this talk I will show that anomalous thresholds arise as a consequence of established S-matrix principles and an extra assumption: analyticity in the mass. I will review how the anomalous threshold appears in the triangle diagram and then derive a nonperturbative version that resums the relevant class of diagrams and how it can be tested.