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, organised by the algebraic and complex geometry research groups in Bochum, Essen, Cologne, and Wuppertal. The seminar meets roughly twice per semester for a full day in Bochum, Essen, Cologne, or Wuppertal. 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

  • SFB/TR 45 "Periods, moduli spaces and arithmetic of algebraic varieties"
  • SFB/TR 191 "Symplectic structures in geometry, algebra and dynamics"

Next Meeting


The next meeting will take place on Friday, April 27th, 2018 in Wuppertal.


  • Hugues Auvray (Orsay): Complete extremal metrics and stability of pairs on Hirzebruch surfaces

    In this talk I will discuss the existence of complete extremal metrics on the complement of simple normal crossings divisors in compact Kähler manifolds, and stability of pairs, in the toric case. Using constructions of Legendre and Apostolov-Calderbank-Gauduchon, we completely characterize when this holds for Hirzebruch surfaces. In particular, our results show that relative stability of a pair and the existence of extremal Poincaré type/cusp metrics do not coincide. However, stability is equivalent to the existence of a complete extremal metric on the complement of the divisor in our examples. It is the Poincaré type condition on the asymptotics of the extremal metric that fails in general. This is joint work with Vestislav Apostolov and Lars Sektnan.

  • Bernd Stratmann (Bochum): Complex and Kähler Structures on Symplectic Reductions

    Given a Hamiltonian action of the real Lie group G on a Kähler manifold (X,\omega) with momentum map \mu, a complex structure and furtheron a Kähler structure are constructed on the symplectic reduction {\mu=0}/G. A notion of a complexification of the real Lie group G and of its orbits is introduced. As a decisive tool, local potentials, i.e. invariant strictly plurisubharmonic functions imposing \omega and \mu, are defined around each point in \mathcal{M}={\mu=0}.

  • Michael Lennox Wong (Essen): Complex Extensions of Compact Kähler Manifolds

    Motivated by a question of Campana--Winkelmann and a twistor space construction in the work of Feix, we look at a certain tautological affine bundle Z over a Kähler manifold X. In general, Z exhibits some "Stein behaviour" though is not necessarily Stein. However, we are able to show, using Mok's uniformization theorem, that for a compact X of non-negative holomorphic bisectional curvature, Z is indeed Stein and is a "good complexification" of X in the sense of Totaro. This is joint work (in progress) with Daniel Greb.


10:30 - 11:30 Wong

11:45 - 12:45 Auvray

12:45 - 14:30 Lunch break

14:30 - 15:30 Stratmann


Bergische Universität Wuppertal
Campus Grifflenberg

All talks will take place in G10, Lecture hall 9.

How to find the lecture hall: see the maps on the following website.


Kevin Fritsch
Ruhr-Universität Bochum
kevin [dot] fritsch [at] rub [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