Event

Talk
Vanishing cycles and monodromy for physical amplitudes
Prof. Dr. Spencer Bloch (University of Chicago)
13 Oct 2015, 17:30 – 18:30

Amplitudes are multiple-valued analytic functions of external momenta in perturbative quantum field theory. The basic local monodromy structure of amplitudes was alread understood by physicists (Laudau, Cutkosky, and others) by the 1960's. Important progress in uniting the physics with the corresponding mathematical theory of vanishing cycles was made by Pham at about the same time, but somehow the story was never completed. I will discuss joint work with D. Kreimer on this topic. In particular, I will explain the physical interpretation of the classical Picard Lefschetz formula (Cutkosky rules) and the relation with Feynman's "i epsilon" rules.