July 8, 2021
Combinatorial classification of semitoric systems
Xiudi Tang, University of Toronto
A four dimensional integrable system is semitoric if one of the components of the momentum map is proper and generates a circle action. We would explain the combinatorial invariants that classify all semitoric systems, which is analogous to the Delzant polytopes for toric systems and the five invariants for simple semitoric systems in the sense that each fiber of the momentum map of the circle action contains at most one singular point of focus-focus type, invented by Pelayo & Vu Ngoc about 10 years ago. This talk is based on joint work with J. Palmer and A. Pelayo, see arXiv:1909.03501.