Humboldt-Universität zu Berlin
Mathem.-Naturwissenschaftliche Fakultät
Institut für Mathematik
Wintersemester 2026-2027
Time: Wednesday 13:15 - 14:45
Room: 3.007 John von Neumann-Haus
Humboldt Arithmetic Geometry Seminar
Seminar: Algebraic Geometry an der FU
| Time | Speaker | |
|---|---|---|
| 28.10.2026, 13:15, 3.007, & 29.10.2026, 15:15, 3.008 | Olivier de Gaay Fortman (Imperial College) | |
| Title: p-Adic obstructions to the integral Hodge conjecture | ||
| Abstract: In these two talks I will report on a joint (ongoing) project with Emiliano Ambrosi. In the first talk, I will give an overview of the theory of prismatic cohomology, as developed by Bhatt and Scholze. I will also formulate our main result, which links de Rham cohomology of varieties in positive characteristic to integral algebraic cycles on complex varieties. In the second talk, I will prove our main result, which proves non-algebraicity of some integral Hodge classes on various classes of complex algebraic varieties. The technique is to use prismatic cohomology and a suitable specialization to positive characteristic, which « degenerates the cohomology » while keeping the variety smooth. All this is joint work with Emiliano Ambrosi. | ||
| 3.11.2026, 13:15, 3.007, & 4.11.2026, 15:15, 1.115 | Charles Vial (Bielefeld) | |
| Title: The fundamental group scheme of globally F-regular varieties | ||
| Abstract: By theorems of Takayama, Xu and Braun, complex projective log Fano varieties are simply connected, and the fundamental group of their regular locus is finite. In positive characteristic, globally F-regular varieties play the role of log Fano varieties, and torsors under finite group schemes replace étale covers. Krah and I showed that the Nori fundamental group scheme of a globally F-regular projective variety is trivial. I will give a proof of this result, and then explain why the Nori fundamental group scheme of the regular locus is finite and linearly reductive. | ||
| 4.11.2026, 13:15, 3.007 | Christian Haase (Freie Berlin) - Seminar X - | |
| Title: Geometric Degenerations with a Polyhedral Flavor | ||
Abstract: In this talk, I will give examples of degeneration techniques in (algebraic) geometry which can be described using objects in
combinatorial convexity. This includes Gröbner degenerations, toric degenerations via Newton-Okounkov bodies or from prime cones in the tropicalisation.
Classical landmark results using such techniques include:
| ||
| 5.11.2026, 16.00, 1.013 | Rahul Pandharipande (ETH Zurich) | |
| Title: New times, new relations | ||
| Abstract: I will present the results (so far) of an ongoing Human-AI collaboration to explore new tautological relations in the moduli of curves. Joint work with S. Canning, B. Kong, D. Peterson, A. Pixton, and J. Schmitt. | ||
| 10.11.2026, 13:15, 3.007, & 11.11.2026, 13:15, 3.007 | Gregorio Baldi (Jussieau) | |
| Title: Algebraic Hodge-Generic Points and the Period Conjecture | ||
| Abstract: Let (\f:X\to S\) be a quasi-projective family of varieties defined over Qbar. We prove that the points of \(S(\bar{Q})\) that are Hodge generic for the variation of Hodge structures associated to f are analytically dense in S. More generally, motivated by the Grothendieck period conjecture and under a large-monodromy assumption, we establish the density of algebraic points at which the periods of the fibre satisfy no unexpected relations of degree at most delta. The main technical input is a new result on relations among solutions of G-operators, based on height estimates of Bombieri and André. This is a joint work with Gal Binyamini and David Urbanik. | ||