Monday, October 5th, 2026
Math Event: Symplectic Geometry, Gauge Theory, and Low-Dimensional Topology Seminar: Roman Krutowski - On Fukaya categories of cotangent bundles of global quotient orbifolds
Time: 12:30 PM - 1:55 PM
Location: Math P-131
Speaker: Roman Krutowski
Abstract: To any global quotient orbifold [X/G] provided by an effective action of a finite group G on a complex manifold X by biholomorphisms, one associates its Hecke algebra. The Hecke algebra is a deformation of the group algebra of the orbifold fundamental group of [X/G]. I will explain that, under some assumptions, the wrapped Fukaya category of the cotangent bundle T^*[X/G] recovers the orbifold Hecke algebra, as the 0-th cohomology of the endomorphisms of a regular fiber. One of the essential tools that we develop is the novel result on the obstructions to smoothings of nodal orbicurves. The talk reports on the joint work with Honda, Tian, and Yuan
Speaker: Roman Krutowski
Abstract: To any global quotient orbifold [X/G] provided by an effective action of a finite group G on a complex manifold X by biholomorphisms, one associates its Hecke algebra. The Hecke algebra is a deformation of the group algebra of the orbifold fundamental group of [X/G]. I will explain that, under some assumptions, the wrapped Fukaya category of the cotangent bundle T^*[X/G] recovers the orbifold Hecke algebra, as the 0-th cohomology of the endomorphisms of a regular fiber. One of the essential tools that we develop is the novel result on the obstructions to smoothings of nodal orbicurves. The talk reports on the joint work with Honda, Tian, and Yuan
Wednesday, October 7th, 2026
Math Event: Algebraic Geometry Seminar: Yongnam Lee - Degree of irrationality of properly elliptic surfaces
Time: 4:00 PM - 5:00 PM
Location:
Speaker: Yongnam Lee
Abstract: In this talk, we discuss the degree of irrationality of properly elliptic surfaces with a section. We establish a sharp lower bound using the canonical bundle formula and the Cayley–Bacharach property. We also study how the degree of irrationality varies in moduli. In particular, a very general properly elliptic surface with a section over a curve of genus at least two has degree of irrationality at least four, whereas certain special families with small holomorphic Euler characteristic have degree of irrationality two. We then investigate the case of properly elliptic surfaces with vanishing holomorphic Euler characteristic. If time permits, we will also discuss properly elliptic surfaces without a section. This is joint work with De-Qi Zhang.
Speaker: Yongnam Lee
Abstract: In this talk, we discuss the degree of irrationality of properly elliptic surfaces with a section. We establish a sharp lower bound using the canonical bundle formula and the Cayley–Bacharach property. We also study how the degree of irrationality varies in moduli. In particular, a very general properly elliptic surface with a section over a curve of genus at least two has degree of irrationality at least four, whereas certain special families with small holomorphic Euler characteristic have degree of irrationality two. We then investigate the case of properly elliptic surfaces with vanishing holomorphic Euler characteristic. If time permits, we will also discuss properly elliptic surfaces without a section. This is joint work with De-Qi Zhang.