June 30, 2026
June 30, 2026
All talks will take place in Room 1.021, CSMB Building
Zum Großen Windkanal 2, 12489 Berlin, Germany
This is a preliminary schedule. It might be subject to changes to the order of the speakers.
All talks will take place in Room 1.021, CSMB Building
Zum Großen Windkanal 2, 12489 Berlin, Germany
This is a preliminary schedule. It might be subject to changes to the order of the speakers.
09:45 – 10:15
10:15 – 11:15
Abstract: The crossing number of Seifert surfaces is defined
by minimising band crossings in projections of surfaces without vertical tangent. In a joint work with Jasmin Joerg and Josefina Villar, we derive lower bounds on the crossing number of Seifert surfaces in terms of the smooth 4-genus and the degree of the Jones polynomial. As we will see, both of these bounds are sharp on interesting families of Seifert surfaces.
11:15 – 11:30
11:30 – 12:30
Abstract: Every knot leaves a trace in the 4-dimensional world. The trace of a knot is the smooth 4-manifold obtained by attaching a 2-handle to the 4-ball along a knot in the 3-sphere. We will introduce the relevant notions and present a strategy to disprove the smooth 4-dimensional Poincaré conjecture by finding knot traces with certain exotic properties. In the second part of the talk, we will discuss different methods to search for such exotic knot traces. This talk will mainly be based on joint work with Jonathan Spreer.
12:30 – 14:30
14:30 – 15:30
Abstract: We show that a small Seifert fibered space with complementary legs does not symplectically bound a rational homology ball for at least one choice of orientation. Our results highlight a sharp contrast with the smooth category, where many more such Seifert fibered spaces are known to bound smooth rational homology balls. As a consequence, we show that a closed, oriented 3-manifold with finite fundamental group admits at most six contact structures, up to isotopy, which are symplectically fillable by rational homology balls. This is a joint work with J. Etnyre and B. Tosun.
15:30 – 16:15
16:15 – 17:15
Abstract: A knot in the 3-sphere is slice if it bounds a smooth disk in the 4-ball. The set of knots modulo slice knots forms an abelian group called the concordance group. Although the study of this group has advanced in recent years, particularly since the advent of Heegaard Floer and Khovanov homology theories, its structure remains mysterious. For instance, the torsion subgroup remains undetermined. In ongoing joint work with Chiara Donatone, Marc Kegel, and Lukas Lewark, we examine how satellite knots and an operation called twisting can help us determine the order of specific knots. As an application, we show that the Conway knot has infinite concordance order.
18:30