# Joint Seminar

# Joint Seminar on Complex Algebraic Geometry and Complex Analysis

(Bochum - Essen - Köln - Münster - 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, Münster, and Wuppertal. 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 the DFG via

- GRK 2553 "Symmetries and Classifying Spaces - analytic, arithmetic, and derived" (Essen)
- SFB/TR 191 "Symplectic structures in geometry, algebra and dynamics" (Bochum-Cologne-Heidelberg)
- ANR-DFG-Projekt QuaSiDy - "Quantization, Singularities, and Holomorphic Dynamics"

# Next Meeting

### DATE AND PLACE

The next meeting will take place on **Friday, May 27th, 2022** for the first time at **WWU Münster** (on-site).

### TALKS

**Markus Banagl (Heidelberg):**Transfer Homomorphisms and Orientation Classes for Singular Spaces

Abstract:

We will discuss the behavior of various orientation and characteristic classes of singular spaces under transfer maps associated to normally nonsingular maps. Two cases arise: Gysin restrictions under embeddings and Becker-Gottlieb type transfers for bundles. In this talk, we will place the emphasis on the latter. The classes considered include topological invariants such as fundamental classes in bordism of singular spaces, in Ranicki's L-homology and Goresky-MacPherson-Cheeger L-classes in rational homology, as well as algebraic classes defined by Brasselet, Schürmann and Yokura. Applications include uniqueness results, obtained jointly with D. Wrazidlo, on L-type characteristic classes for algebraic subvarieties of Grassmannians, e.g. Schubert varieties.**Francesco Bei (Sapienza):**On weak Kähler hyperbolic manifolds and geometric applications

Abstract:

Kähler hyperbolic manifolds were introduced by Gromov around thirty years ago. In his seminal paper he showed that this class of Kähler manifolds enjoys several remarkable properties: for instance they are of general type, Kobayashi hyperbolic and their $L^2$-Hodge numbers $h^{p,q}_{(2)}$ are positive if and only if $p = q$. In this talk I will report about a recent joint work with S. Diverio, P. Eyssidieux and S. Trapani where we introduced some weak versions of Kähler hyperbolicity. I will show how some of the properties proved by Gromov for Kähler hyperbolic manifolds remain true in our more general setting and I will explain various geometric applications. In particular I will describe how these ideas allow to verify some aspects of the Lang conjecture for Kähler hyperbolic manifolds.**Nicolina Istrati (Marburg):**On the Bott-Chern Cohomology of Vaisman manifolds

Abstract:

Vaisman manifolds are complex manifolds which can be endowed with a special type of a Hermitian structure, namely a locally conformally Kähler metric with parallel Lee form. Typical examples are given by holomorphic principal torus bundles over a projective manifold with prescribed characteristic class. More generally, the geometry of Vaisman manifolds is closely related to Kählerian geometry, as these manifolds always come endowed with a natural transversally Kähler foliation. However, Vaisman manifolds do not satisfy the $dd^c$-lemma, therefore it is interesting to study their Bott-Chern cohomology, which is then a refined invariant. In this talk, I will explain how one can express this cohomology in terms of the basic cohomology with respect to the foliation, and in particular show that the numerical obstructions to the $dd^c$-lemma can be arbitrarily high. This is based on joint work with Alexandra Otiman.

### SCHEDULE

**10:30 - 11:30** Istrati

**11:45 - 12:45** Bei

**afterwards** Lunch break

**14:30 - 15:30** Banagl

### VENUE

All talks will take place in

**room SRZ 216/217**on the second floor of the seminar building located at

**Orléans-Ring 12**in

**Münster**. Please find detailed information how to find the Seminarraumzentrum (SRZ) on the following website.

We will additionally stream the talks via ZOOM. Access data will be distributed via the usual channels. In case you don't have the information and want to participate, please write an eMail to one of the organisers in order to gain access.

# Organisers

Daniel Greb

Universität Duisburg-Essen

daniel [dot] greb [at] uni-due [dot] de

Stéphanie Cupit-Foutou

Ruhr-Universität Bochum

stephanie [dot] cupit [at] ruhr-uni-bochum [dot] de

Ursula Ludwig

WWU Münster

ursula [dot] ludwig [at] uni-muenster [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