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Interactions between symplectic geometry, combinatorics and number theory (14722.0073)


The "ColMar" Interactions




The seminar "Interactions" joins the teams of two universities: that of Cologne, and that of Marburg, therefore the name "ColMar** Interactions". The goal is to explain some very recent developments in the field of equivariant topology and equivariant symplectic geometry.

The organisers are:

Oliver Goertsches (

Panagiotis Konstantis (

myself (

The talks will be on Friday from 2:30 to 3:30 PM Cologne time (CEST). See below for the list of the available Fridays.

Every talk will be streamed on Zoom and, if the speaker is "local", the talks will be held in person.


Talks in the winter semester 2023/2024:

27.10.23: Nicholas Lindsay (University of Cologne), Exotic almost complex circle actions on 6-manifolds

03.11.23: Leonor Godinho (Instituto Superior Tecnico, Lisbon), On a symplectic generalization of a Hirzebruch problem

17.11.23: Taras Panov (Moscow State University), Holomorphic foliations on complex manifolds with torus actions

24.11.23: Liat Kessler (University of Haifa), Extending cyclic actions to circle actions, using combinatorial, holomorphic and number-theoretic methods.

01.12.23: Ping Li (Fudan University, Shanghai), The complex genera, symmetric functions and multiple zeta values

15.12.23: Ana Cannas da Silva (ETH Zurich), Toric Lagrangians

12.01.24: Yunhyung Cho (Sungkyunkwan University), Maximal tori in the Hamiltonian diffeomorphism groups and their mutations

19.01.24: Rebecca Goldin (George Mason University), On positivity for flag manifolds and Hessenberg spaces


Talks in the summer semester 2023:

19.05.23: Mikiya Masuda (Osaka City University), Topology of regular semisimple Hessenberg varieties and related topics

09.06.23: Daniele Sepe (Universidade Federal Fluminense), On some integrable systems on complexity one spaces​

14.07.23: Seonjeong Park (Jeonju University), Classification of toric Schubert varieties


Talks in the winter semester 2022/2023:

11.11.22: Jeffrey Carlson (Imperial College London), The topology of Gelfand–Zeitlin fibers

25.11.22: Maarten Mol (MPI Bonn), Stratification of the transverse momentum map

02.12.22: Donghoon Jang (Pusan National University), Almost complex torus manifolds - graphs, Hirzebruch genera, and a problem of Petrie type

13.01.22: Masoumeh Zarei (U. Münster), Alexandrov spaces, symmetry and positive curvature

20.01.23: Yichen Liu (University of Illinois Urbana-Champaign), Extending complexity-1 spaces to toric manifolds

27.01.23: Matthias Franz (University of Western Ontario), The cohomology rings of real toric spaces and smooth real toric 

03.02.23: Shintaro Kuroki (Okayama University of Science), TBA


* In the summer semester 2022 the seminar was organised by the University of Marburg only. Here you can find the link to the seminar website for this semester:


* Previous talks in the winter semester 2021/2022:

21.10.21, 14:30-16:00: Nicholas Lindsay (U. of Cologne), "Hamiltonian S^1-actions on complete intersections"

17.11.21, 12:30-14:00: Anton Ayzenberg (HSE University), "Face posets of equivariantly formal torus actions"

09.12.21, 14:30-16:00: Chris McDaniel (Endicott College), "A GKM Description for the Equivariant Coinvariant Ring of a Pseudo Reflection Group"

16.12.21, 14:30-16:00: Lisa Jeffrey (U. of Toronto), "Poisson maps between character varieties: gluing and capping"

* Link to talks in the academic year 2020/2021:


** It is also worth noticing that in Italian "colmare" means "to bridge", and we like bridges, because they allow interactions...



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