Joint Seminar on Complex Algebraic Geometry and Complex Analysis
(Bochum - Essen - Köln - Wuppertal)

Photo by Max Greve and Timo Bobert

The Seminar

The "Joint Seminar on Complex Algebraic Geometry and Complex Analysis" is a research seminar, run by the algebraic and complex geometry research groups in Bochum, Essen, Cologne, and Wuppertal since 2013. The seminar meets roughly twice per semester for a full day at one of the participating departments. There are three talks per meeting, both by invited guests and by speakers from the organising universities. We aim to leave ample room for discussions.

The talks are open for everyone. Contact one of the organisers if you are interested in attending the meeting. We have some funds that might help to support travel for some junior participants.

Meetings of the seminar are partially supported by

• DFG-GRK 2553 "Symmetries and Classifying Spaces - analytic, arithmetic, and derived" (Essen)
• DFG-SFB/TR 191 "Symplectic structures in geometry, algebra and dynamics" (Bochum-Cologne-Heidelberg)

Next Meeting

DATE AND PLACE

The next meeting will take place on Friday, January 30th, 2026 at Universität Duisburg-Essen.

TALKS

• Roger Bielawski (Hannover): Towards hypercomplex varieties and spaces
  
  Abstract:
  A hypercomplex manifold is a real manifold admitting a triple of integrable complex structures which behave algebraically as the generators i,j,k of quaternions. Such manifolds (often admitting a compatible Riemannian metric, and known then as hyperkaehler) are ubiquitous in high energy physics and in several areas of mathematics. On the other hand, since there is no ring of "hypercomplex functions", it is unclear how to define singular hypercomplex objects. In my talk I shall discuss the definitions previously proposed by Verbitsky and Joyce, and suggest an alternative one.



• Victoria Hoskins (UDE): Relative non-reductive GIT and moduli of quivers with multiplicities
  
  Abstract:
  I will report on joint work on relative non-reductive geometric invariant theory with E. Hamilton and J. Jackson, and describe some new moduli spaces that can be constructed using these methods. In particular, I will focus on representations of a quiver with multiplicities, which generalise quiver representations by replacing the base field with truncated polynomial rings. Representations of quivers with multiplicities arise in the study of moduli or irregular meromorphic connections on the projective line and in the study of symmetrisable Kac-Moody Lie algebras. Together with J. Jackson and T. Vernet, we construct moduli spaces of certain semistable quiver representations with multiplicities and analogues of Nakajima quiver varieties for a quiver with multiplicities. In favourable situations, we also prove their cohomology carries a pure Hodge structure, analogously to the classical case without multiplicities.



• Claudio Llosa (KIT): TBA
  
  Abstract:
  TBA

SCHEDULE

10:30 - 11:30 Bielawski

11:45 - 12:45 Hoskins

afterwards Lunch

14:30 - 15:30 Llosa

VENUE

Talks will take place in seminar room S01 B29 in building S06 on the main Essen campus. A map showing the building on the campus be found here. The building is close to the underground station "Universität Essen" and a new university car park (both visible on the map).

Organisers

Stéphanie Cupit-Foutou
Ruhr-Universität Bochum
stephanie [dot] cupit [at] ruhr-uni-bochum [dot] de

Daniel Greb
Universität Duisburg-Essen
daniel [dot] greb [at] uni-due [dot] de

George Marinescu
Universität zu Köln
gmarines [at] math [dot] uni-koeln [dot] de

Jean Ruppenthal
Bergische Universität Wuppertal
jean [dot] ruppenthal [at] math [dot] uni-wuppertal [dot]de

Past Meetings

26.4.2013, Bochum: Tim Kirschner, Christian Miebach, Henrik Seppänen

28.6.2013, Wuppertal: Rafael Andrist, Immanuel Stampfli, Matei Toma

22.11.2013, Bochum: Sébastien Boucksom, Egmont Porten, Sönke Rollenske

24.1.2014, Wuppertal: Clemens Jörder, Helge Ruddat, Jörg Winkelmann

16.5.2014, Bochum: Alberto Abbondandolo, Judith Brinkschulte, Julius Ross

20.6.2014, Wuppertal: Julie Déserti, Slawomir Dinew, Slawomir Rams

24.10.2014, Bochum: Henri Guenancia, Shulim Kaliman, Adriano Tomassini

15.12.2014, Wuppertal: Richard Lärkäng, Christian Miebach, Marco Spinaci

7.5.2015, Essen: Brent Doran, Erwan Rousseau, Emanuel Scheidegger

15.6.2015, Bochum: Roya Beheshti, Daniel Greb, Hossein Raufi

27.11.2015, Wuppertal: Francesco Bei, Kai Cieliebak, Tyson Ritter

1.2.2016, Essen: Ursula Ludwig, George Marinescu, Wenhao Ou

25.4.2016, Wuppertal: Gian Maria Dall’Ara, Christian Lehn, Luca Tasin

26.6.2016, Cologne: Chin-Yu Hsiao, Stefan Nemirovski, Nikhil Savale

25.11.2016, Bochum: Ana-Maria Brecan, Antonio di Scala, Dan Popovici

27.1.2017, Essen: Tim Kirschner, Viêt Anh Nguyên, Stefan Schreieder

21.4.2017, Wuppertal: Vicente Cortés, Philipp Naumann, Markus Reineke

7.7.2017, Cologne: Roger Bielawski, Dan Coman, Martin Schwald

3.11.2017, Bochum: Junyan Cao, Sönke Rollenske, Robert Szöke

1.2.2018, Essen: Gilberto Bini, Ruadhaí Dervan, Hendrik Herrmann

27.4.2018, Wuppertal: Hugues Auvray, Bernd Stratmann, Michael Lennox Wong

6.7.2018, Cologne: Turgay Bayraktar, Jarek Buczynski, Andrew Dancer

23.11.2018, Bochum: Ben Anthes, Kevin Fritsch, Ariyan Javanpeykar

18.1.2019, Essen: André Belotto, Andreas Höring, Valdemar Tsanov

12.4.2019, Wuppertal: Ya Deng, Christian Miebach, Duc Viet Vu

5.7.2019, Cologne: Tien-Cuong Dinh, Xiaonan Ma, Nessim Sibony

21.11.2019, Bochum: Patrick Graf, Ulrike Rieß, Jonas Stelzig

16.1.2020, Essen: Anda Degeratu, Takeo Ohsawa, Mihai Paun

14.5.2020, Wuppertal (via ZOOM): Lynn Heller, Simone Marchesi, Jan Swoboda

16.7.2020, Cologne (via ZOOM): Shin-ichi Matsumura, Sönke Rollenske, Lars Martin Sektnan

17.11.2020, Bochum (via ZOOM): Rafael Andrist, Nicholas Buchdahl, Eleonora di Nezza

29.1.2021, Essen (via ZOOM): Robert Berman, Simone Diverio, Ilaria Mondello

7.5.2021, Wuppertal (via ZOOM): Siarhei Finski, Laszlo Lempert, Katharina Neusser

18.6.2021, Cologne (via ZOOM): Gordon Heier, Louis Ioos, Ursula Ludwig

26.11.2021, Bochum: Nikhil Savale, Martin Schwald, Jörg Winkelmann

11.03.2022, Essen: Narasimha Chary Bonala, Matteo Costantini, Josias Reppekus

27.05.2022, Münster: Markus Banagl, Francesco Bei, Nicolina Istrati

20.06.2022, Essen: Workshop organised by JS organisers

25.11.2022, Wuppertal: Masanori Adachi, Laurentiu Maxim, Sara Torelli

20.1.2023, Cologne: Fabrizio Bianchi, Tobias Harz, Susanna Zimmermann

28.4.2023, Bochum: Hans-Joachim Hein, Silvia Sabatini, Richard Wentworth; 10 year celebration

7.7.2023, Essen: Ravjot Kohli, Thomas Kurbach, Niklas Müller

27.10.2023, Münster: Stefan Nemirovski, Shu Shen, Carolina Tamborini

19.2.2024, Wuppertal: Bo Berndtsson, Ana Botero, Jörg Winkelmann

26.4.2024, Cologne: Cécile Gachet, Christian Lehn, Johannes Scheffler

12.7.2024, Bochum: Stéphanie Cupit-Foutou, Bingxiao Liu, Jörg Schürmann

6.12.2024, Essen: Michele Ancona, Siarhei Finski, Alice Garbagnati

25.2.2025, Essen: Judith Brinkschulte, Matteo Costantini

11.4.2025, Wuppertal: Jun-Muk Hwang, Takayuki Koike, Matilde Maccan

18.7.2025, Bochum: Workshop on Transformation Groups, organised by JS organisers

21.11.2025, Cologne: Max Jahnke, Roland Púček, Shengxuan Zhou