Oberseminar über komplexe Geometrie

Dienstag 21.05.2024

10:00 Uhr    IA 1/53

Christian Zöller (RUB), Der lokale Struktursatz für Hamiltonsche Wirkungen auf kompakten Kähler-Mannigfaltigkeiten



Mittwoch 17.04.2024

12:00 Uhr    IA 1/109

Shang Li (Paris), Wonderful compactification over an arbitrary base scheme

Abstract: Wonderful compactifications of adjoint reductive groups over an algebraically closed field play an important role in algebraic geometry and representation theory. In this talk, we will construct an equivariant compactification for adjoint reductive groups over arbitrary base schemes, which parameterize classical wonderful compactifications of De Concini and Procesi as geometric fibers. Our construction is based on a variant of the Artin–Weil method of birational group laws. In particular, our construction gives a new intrinsic construction of wonderful compactifications. If time permits, we will also discuss several applications of our compactification in the study of torsors under reductive group schemes.


Mittwoch 17.01.2024

10:00 Uhr    IA 1/75

Johanna Bimmermann (RUB), Capacities of disk tangent bundles

Abstract: In general rather little is known about symplectic capacities of open subsets of cotangent bundles. In this talk I will discuss methods to compute the Gromov width and the Hofer—Zehnder capacity of disk tangent bundles and demonstrate these methods for certain homogenous spaces (namely spheres and projective spaces). The key observation is that in these cases the disk bundle sits as complement of a divisor inside a coadjoint orbit. This makes it possible to explicitly construct symplectic embeddings of balls for the lower bound and find non-vanishing Gromov—Witten invariants for the upper bound.


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