Humboldt-Universität zu Berlin
Mathem.-Naturwissenschaftliche Fakultät
Institut für Mathematik
Sommersemester 2026
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 | |
|---|---|---|
| 22.04.2026, 13:15 - 14: 45 | Federico Moretti (Stony Brook) | |
| Title: Picard bundles and degree of irrationality of jacobians | ||
| Abstract: The degree of irrationality of a projective variety is the smallest degree of a dominant rational map to projective space of the same dimension. I explain a vector-bundle approach via kernel bundles, implying that a globally generated bundle with positive top Chern class gives an immediate upper bound. I then study twists of Picard bundles and obtain that the degree of irrationality of any genus \(g\) Jacobian is at most \(2^g\). This is based on joint work with Andrés Rojas. | ||
| 28.04.2026, 15 - 16, Room: 1.013 | Daniel Huybrechts (Bonn) - COLLOQUIUM | |
| Title : Brauer groups: From number theory to (hyperkähler) geometry | ||
| Abstract: The Brauer group of a field was introduced a century ago, but it still holds many secrets. It started out as an object in number theory, with the theorem of Brauer—Hasse—Noether as a first highlight, and was later generalised by Grothendieck to a geometric setting. ln this talk, I will sketch certain aspects of the history that are relevant to recent developments in geometry and Hodge theory with a special emphasis on hyperkähler geometry. | ||
| 29.04.2026, 13:15 - 14:45 | Theodosis Alexandrou (HU Berlin) | |
| Title: A surface with representable \(CH_{0}\)-group but no universal zero-cycle. | ||
| Abstract: We introduce a new obstruction to the existence of a universal 0-cycle on a smooth projective complex variety. As an application, we construct a smooth projective complex surface whose Chow group of 0-cycles is representable but which does not admit a universal 0-cycle. This provides a two-dimensional analogue of Voisin’s recent threefold counterexample to a question of Colliot-Thélène. As a further consequence, we exhibit the first example of a smooth projective threefold of Kodaira dimension zero carrying a non-torsion Hodge class of degree 4 that is not algebraic. The construction relies on the geometry of bielliptic surfaces of type 2. | ||