September 15-16, 2026 

Ruhr-Universität Bochum 

                                                                                                                                                                                                                                                                                                                                                                      RUB, Marquard

Minicourses on the b-semiampleness conjecture by 

Ben Bakker (Chicago)

Mirko Mauri (Jussieu)

Research Talks by 

Marta Benozzo (Jussieu)

Benoît Cadorel (Nancy)

Vasily Rogov (Leipzig)

Calla Tschanz (Bochum)

Titles and abstracts

B. Bakker & M. Mauri: Semiampleness in Hodge theory and compact moduli spaces of Calabi--Yau varieties

It is conjectured that every algebraic variety admits a decomposition into varieties with positive, negative, or trivial canonical bundle. While the moduli theory in the cases of positive and negative canonical bundle is by now well understood, the Calabi--Yau case remains substantially more elusive. By the local Torelli theorem, Hodge structures of Calabi--Yau varieties distinguish locally Calabi--Yau varieties. However, due to their inherently transcendental nature, leveraging these structures in the construction of compact algebraic moduli spaces presents significant difficulties. The problem can be reformulated in terms of the semiampleness of the Hodge line bundle associated with certain Calabi--Yau variations of Hodge structure. This property has recently been established in joint work with Benjamin Bakker, Stefano Filipazzi, and Jacob Tsimerman. The result constitutes a key input in the resolution of two long-standing conjectures: Griffiths’ conjecture on functorial compactifications of images of period maps, and the b-semiampleness conjecture of Kawamata, Shokurov and Prokhorov. The proof relies crucially on o-minimality, which provides the perfect framework for taming the transcendence of Hodge theory, and marks the first application of o-minimal methods in birational geometry. 

V. Rogov: Higher Albanese manifolds and nilpotent fundamental groups.

Higher Albanese manifolds and higher Albanese maps were proposed by Hain and Zucker as generalisations of the classical Albanese. I am going to review their construction, discuss its topological and complex analytic properties, and explain how it fits into the general philosophy of o-minimality in Hodge theory. Finally, I will talk about some applications to the question of which nilpotent groups can arise as fundamental groups of complex algebraic varieties.

C. Tschanz: From logarithmic Hilbert schemes to degenerations of hyperkähler varieties

In this talk, I will discuss my previous work on constructing explicit models of logarithmic Hilbert schemes. This relates to work or Li-Wu on expanded degenerations, Gulbrandsen-Halle-Hulek on degenerations of Hilbert schemes of points and Maulik-Ranganathan on logarithmic Hilbert schemes. The constructions I consider are local. I will then explain how we globalise these in joint work with Shafi and apply them to construct minimal type III degenerations of hyperkähler varieties, namely Hilbert schemes of points on K3 surfaces.

Schedule

Venue

All talks will take place at Ruhr-Universität Bochum, in Seminar Room IC 03/604 (which means: building IC, level 03, room 604); a campus map can be found here.

Registration

Please tell us if you plan to participate by filling out the following form. Please indicate on the form if you want to give a contributed talk on the topic of the workshop. In case of questions, please contact one of the organisers.

Organisers

Cécile Gachet (RUB)

Daniel Greb (UDE)

Christian Lehn (RUB)