Seminars and Colloquia by Series

Surgeries on knots and tight contact structures

Series
Geometry Topology Seminar
Time
Monday, December 1, 2025 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Shunyu WanGeorgia Tech

The existence and nonexistence of tight contact structures on the 3-manifold are interesting and important topics studied over the past thirty years. Etnyre-Honda found the first example of a 3-manifold that does not admit tight contact structure, and later Lisca-Stipsicz extended their result and showed that a Seifert fiber space admits a tight contact structure if and only if it is not the smooth (2n − 1)-surgery along the T(2,2n+1) torus knot for any positive integer n.

Surprisingly, since then no other example of a 3-manifold without tight contact structure has been found. Hence, it is interesting to study if all such manifolds, except those mentioned above, admit a tight contact structure. Towards this goal, I will discuss the joint work with Zhenkun Li and Hugo Zhou about showing any negative surgeries on any knot in S^3 admit a tight contact structure.  

Bordered contact invariants and half Giroux torsion

Series
Geometry Topology Seminar
Time
Monday, November 24, 2025 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Konstantinos VarvarezosUGA

Giroux torsion is an important class of contact structures on a neighborhood of a torus, which is known to obstruct symplectic fillability. Ghiggini conjectured that half Giroux torsion along a separating torus always results in a vanishing Heegaard Floer contact invariant hence also obstructs fillability. In this talk, we present a counterexample to that conjecture. Our main tool is a bordered contact invariant, which enables efficient computation of the contact invariant.

Reeb dynamics of contact toric structures and concave boundaries of plumbings

Series
Geometry Topology Seminar
Time
Monday, November 17, 2025 - 16:30 for 1 hour (actually 50 minutes)
Location
Boyd 322, University of Georgia
Speaker
Jo NelsonRice University

Algebraic torsion is a means of understanding the topological complexity of certain homomorphic curves counted in some Floer theories of contact manifolds.  This talk focuses on algebraic torsion and the contact invariant in embedded contact homology, useful for obstructing symplectic fillability and overtwistedness of the contact 3-manifold, but mostly left unexplored. We discuss results for concave linear plumbings of symplectic disk bundles over spheres admitting a concave contact boundary, whose boundaries are contact lens spaces.  We explain our curve counting methods in terms of the Reeb dynamics and their parallel with the topological contact toric description of these lens spaces. This talk is based on joint work with Aleksandra Marinkovic, Ana Rechtman, Laura Starkston, Shira Tanny, and Luya Wang.  Time permitting, we will discuss exploration of our methods to find nonfillable tight contact 3-manifolds obtained from more general plumbings.

Anchored symplectic embeddings

Series
Geometry Topology Seminar
Time
Monday, November 17, 2025 - 15:00 for 1 hour (actually 50 minutes)
Location
Boyd 322, University of Georgia
Speaker
Agniva RoyBoston College

Symplectic manifolds exhibit curious behaviour at the interface of rigidity and flexibility. A non-squeezing phenomenon discovered by Gromov in the 1980s was the first manifestation of this. Since then, extensive research has been carried out into when standard symplectic shapes embed inside another -- it turns out that even when volume obstructions vanish, sometimes they cannot. A mysterious connection to Markov numbers, a generalization of the Fibonacci numbers, and an infinite staircase, is exhibited in the study of embeddings of ellipsoids into balls. In other cases ingenious constructions such as folding have been invented to find embeddings. In recent work with Hutchings, Weiler, and Yao, I studied the embedding problem for four-dimensional symplectic shapes in conjunction with the question of existence of symplectic surfaces (called anchors) inside the embedding region. In this talk I will survey some of the results and time permitting, discuss the ideas behind the proof, and applications of these techniques to understanding isotopy classes of embeddings.

An Excision Theorem in Heegaard Floer Theory

Series
Geometry Topology Seminar
Time
Monday, November 10, 2025 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Neda BagherifardGeorgia Tech

In this talk, I will describe an excision construction for 3-manifolds and explain how (twisted) Heegaard Floer theory can be used to obstruct 3-manifolds from being related via such constructions. I will also discuss how the excision formula can be applied to compute twisted Heegaard Floer homology groups for specific 3-manifolds obtained by performing surgeries on certain links, including some 2-bridge links.

New perspectives on Heegaard Floer satellite operators

Series
Geometry Topology Seminar
Time
Monday, November 3, 2025 - 14:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Ian ZemkeUniversity of Oregon

Satellite operations are one of the most basic operations in knot theory. Many researchers have studied the behavior of knot Floer homology under satellite operations. Most of these results use Lipshitz, Ozsvath and Thurston's bordered Heegaard Floer theory. In this talk, we discuss a new technique for studying these operators, and we apply this technique to a family of operators called L-space operators. Using this theory, we are able in many cases to give a simple formula for the behavior of the concordance invariant tau under such operators. This formula generalizes a large number of existing formulas for the behavior of tau under satellite operations (such as cabling, 1-bridge braids and generalized Mazur patterns), and also has a number of topological applications. This is joint work with Daren Chen and Hugo Zhou.

Yang—Mills gauge theory and Dehn surgery problems

Series
Geometry Topology Seminar
Time
Monday, October 27, 2025 - 16:30 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Aliakbar DaemiWashington University in St. Louis

In their celebrated work, Gordon and Luecke proved that knots in the three-dimensional sphere are determined by their complements. Their result inspired several conjectures seeking to generalize the theorem, including "Cosmetic surgery conjecture" proposed by Gordon and the "Knot complement problem for null-homotopic knots" proposed by Boileau. In this talk, I will discuss applications of tools from Yang—Mills gauge theory to these Dehn surgery problems.

Dehn–Seidel twists on configurations of Lagrangian spheres in K3 surfaces

Series
Geometry Topology Seminar
Time
Monday, October 27, 2025 - 15:00 for 1 hour (actually 50 minutes)
Location
Skiles 006
Speaker
Juan Munoz-EchanizStony Brook University

On a closed, simply-connected, symplectic 4-manifold, the Dehn–Seidel twists on Lagrangian spheres and their products provide all known examples of non-trivial elements in the symplectic mapping class group. However, little is known in general about the relations that may hold among Dehn–Seidel twists. 

I will discuss the following result: on a symplectic K3 surface, the squared Dehn--Seidel twists on Lagrangian spheres with distinct fundamental classes are algebraically independent in the abelianization of the (smoothly-trivial) symplectic mapping class group. In a particular case, this establishes an abelianized form of a Conjecture by Seidel and Thomas on the faithfulness of certain Braid group representations in the symplectic mapping class group of K3 surfaces. The proof makes use of Seiberg--Witten gauge theory for families of symplectic 4-manifolds.

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