## Math Calendar

Tuesday, May 17, 2022
11:00-12:00
HFG-610
Algebraic Geometry talk
Michele Graffeo - Moduli spaces of Z/kZ-constellations over the affine plane
It is a classical result that, for any finite subgroup G of SL(n,C), for n=2,3, there exists (at least) one crepant resolution of the singularity "affine n-space modulo G-action". When G is abelian, thanks to a work of Craw and Ishii, any such resolution can be interpreted as the fine moduli space of certain coherent sheaves, called G-constellations, which are stable with respect to a GIT stability condition. In my talk I will introduce the above mentioned notions and I will talk about some combinatorial objects that I have introduced to describe the two-dimensional setting. If time permits, I will also explain some three-dimensional phenomena.
Wednesday, May 18, 2022
13:15-14:15
BBG-0.17
Master thesis defense
Jens de Vries- C*-Actions and Takai Duality

Daily Supervisor: Dr. Henrik Kreidler(University of Wuppertal, Germany)

Local Supervisor: Dr. Karma Dajani

Abstract: The study of classical dynamical systems $(G,\Omega)$ dealswith actions of locally compact Hausdorff groups $G$ on locally compactHausdorff spaces $\Omega$. It is long recognized that classical dynamicalsystems can be succesfully studied via C*-algebras. A C*-action is atopological group homomorphism $\alpha$ from a locally compact Hausdorff group$G$ to $\Aut(A)$, where $\Aut(A)$ is the automorphism group of a C*-algebra $A$endowed with the topology of pointwise convergence. The C*-actions involvingcommutative C*-algebras precisely model the classical dynamical systems.

Every C*-action gives rise to a C*-algebra, called thecrossed product, which encodes a lot of information about the C*-action. Usingcrossed products and duality theory for abelian locally compact Hausdorffgroups $G$ one can develop a certain duality theory for C*-actions $\alpha$.Just as Pontryagin duality describes the second dual of $G$, Takai dualitydescribes the second dual of $\alpha$. In essence, one recovers a C*-actionfrom its crossed product up to tensoring with another C*-action.

Tuesday, May 24, 2022
16:00-17:00
HFG Library
MI talks
Jack Davies - Derived Hecke operators
TBA

Website of the UGC seminar (and the pure side of the MI-talks): http://utrechtgeometrycentre.nl/ugc-seminar/
Practical details will be sent by email to the staff and student mailing lists a few days before the event.
Friday, May 27, 2022
11:00-12:00
Hans Freudenthalgebouw 0.01a
History of mathematics guest lecture
Klaus Volkert (Universität Wuppertal) - The three mathematical friends on geometry
TBA
Monday, May 30, 2022
12:15-13:15
PhD Defense Jetze Zoethout
Thursday, June 2, 2022
15:30-17:30
Nijmegen HG03.054
TopICS
Topology Intercity Seminar

Stefan Schwede

Title: TBA.

Abstract: TBA.
Monday, June 13, 2022
12:15-13:15
PhD Defense Sergej Monavari
Thursday, June 16, 2022
12:00-13:00
BYOL MI
15:30-17:30
Nijmegen HG03.085
TopICS
Topology Intercity Seminar

TBA

Title: TBA.

Abstract: TBA.
Saturday, June 18, 2022
10:00-18:00
Mini-Conference on the History of Constructive Geometry
Speakers:

• Sandra Bella (Laboratoire SPHERE, Université de Paris)
• Viktor Blåsjö (Utrecht University)
• Davide Crippa (Ca' Foscari University of Venice)
• Jeanine Daems (Hogeschool Utrecht)
• Ad Meskens (Artesis Plantijn University College of Antwerp)
• Nicolas Michel (Utrecht University)
• Ivahn Smadja (Université de Nantes)

Website of the event: https://utrechtgeometrycentre.nl/mini-conference-on-the-history-of-constructive-geometry/
Tuesday, June 21, 2022
16:00-17:00
HFG Library
MI talks
Sergej Monavari - TBA
TBA

Website of the UGC seminar (and the pure side of the MI-talks): http://utrechtgeometrycentre.nl/ugc-seminar/
Practical details will be sent by email to the staff and student mailing lists a few days before the event.
Friday, June 24, 2022
09:00-17:00
Koningsbergergebouw, Atlas room
Mini-Workshop on Symplectic Geometry

This mini-workshop is aimed at researchers, Ph.D. students, and advanced master's students working in symplectic geometry and related areas. It is organized jointly with the Vrije Universiteit Amsterdam.

This is the tenth workshop that we are organizing. Building on a pre-corona tradition, we plan to organize these mini-workshops again biannually. The goal is to strengthen the symplectic community of the Netherlands and to connect it with abroad. Topics include Hamiltonian dynamics, the symplectic embedding question, holomorphic curves, and Floer homology.

Website: https://webspace.science.uu.nl/~zilte001/symplectic_2022_06_24/index.php

### Speakers

Umberto Hryniewicz (Aachen)