Other area seminars. Our email list. Archive of previous semesters
Fall 2021
Date  Time (Eastern)  Speaker  Title 

September 17 
11 am (Note nonstandard time) 
Proper actions of 3manifold groups on finite product of quasitrees 

September 24 
2 pm 
The Khovanov homology of slice disks 

October 1 
2 pm 
Braids, fibered links, and annular Khovanov homology 

October 8 
2 pm 
Geography of spanning surfaces 

October 15 
2 pm 
Endperiodic homeomorphisms and volumes of mapping tori 

October 22 
2 pm 
Reeb flows transverse to foliations 

November 5 
11 am (Note nonstandard time) 
Searching for geometric finiteness using surface group extensions 

November 5 
2 pm (Note double header) 
Knotted surfaces with infinite cyclic knot group 

November 12 
11 am (Note nonstandard time) 
A reboot of the theory of braids and knots: the Thompson groups as knot constructors 

November 19 
2 pm 
Length, Stable Commutator Length, and Hyperbolic Geometry 

December 3 
11 am (Note nonstandard time) 
Quick quantum invariants of rotational tangles (handout) 

December 10 
2 pm 
Peg Problems 
Abstracts
Wenyuan Yang, Peking University
Title: Proper actions of 3manifold groups on finite product of quasitrees
Abstract: Let M be a compact, connected, orientable 3manifold. In this talk, I will study when the fundamental group of M acts properly on a finite product of quasitrees. Our main result is that this is so exactly when M does not contain Sol and Nil geometries. In addition, if there is no $\widetilde{SL(2, \mathbb{R})}$ geometry either, then the orbital map is a quasiisometric embedding of $\pi_1(M)$. This is called property (QT) by BestvinaBrombergFujiwara, who established it for residually finite hyperbolic groups and mapping class groups. The main step of our proof is to show property (QT) for the classes of CrokeKleiner admissible groups and of relatively hyperbolic groups under natural assumptions. Accordingly, this yields that graph 3manifold and mixed 3manifold groups have property (QT). This represents joint work with N.T. Nguyen and S.Z. Han.
Isaac Sundberg, Bryn Mawr College
Title: The Khovanov homology of slice disks
Abstract: A smooth, oriented surface that is properly embedded in the 4ball can be regarded as a cobordism between the links it bounds, namely, the empty link and its boundary in the 3sphere. To such link cobordisms, there is an associated linear map between the Khovanov homology groups of the boundary links, and moreover, these maps are invariant, up to sign, under boundarypreserving isotopy of the surface. In this talk, we review these maps and use their invariance to understand the existence and uniqueness of slice disks and other surfaces in the 4ball. This reflects joint work with Jonah Swann and, separately, with Kyle Hayden.
Gage Martin, Boston College
Title: Braids, fibered links, and annular Khovanov homology
Abstract: BirmanHilden give a construction that relates braid closures with certain fibered links via taking a branched double cover. In this talk we will see how the construction can be used to give topological applications of annular Khovanov homology. As an example we will use the BirmanHilden construction to show that annular Khovanov homology detects a specific 4braid representative of the unknot. This is joint work with Fraser Binns.
Title: Geography of spanning surfaces
Abstract: The geography problem for spanning surfaces asks for a classification of all pairs of slope and euler characteristic which can be realised by a spanning surface for a given knot in the 3sphere. It is enough to understand the meridionally essential onesided spanning surfaces, a somewhat larger class of surfaces than the geometrically essential spanning surfaces. We will discuss the existence of such onesided surfaces, and give an algorithmic solution to the geography problem.
Title: Endperiodic homeomorphisms and volumes of mapping tori
Abstract: I will discuss volumes of mapping tori associated to irreducible endperiodic homeomorphisms of certain infinitetype surfaces, inspired by a theorem of Brock (in the finitetype setting) relating the volume of a mapping torus to the translation distance of its monodromy on the pants graph. This talk represents joint work with Elizabeth Field, Heejoung Kim, and Chris Leininger.
Jonathan Zung, Princeton University
Title: Reeb flows transverse to foliations
Abstract: Eliashberg and Thurston showed that (almost all) C^2 taut foliations on 3manifolds can be approximated by tight contact structures. I will explain a new approach to this theorem which allows one to control the resulting Reeb flow and hence produce many hypertight contact structures. Along the way, I will explain how harmonic transverse measures may be used to understand the holonomy of foliations.
Title: Knotted surfaces with infinite cyclic knot group.
Abstract: This talk will concern embedded surfaces in 4manifolds for which the fundamental group of the complement is infinite cyclic. Working in the topological category, necessary and sufficient conditions will be given for two such surfaces to be isotopic. This is based on joint work with Mark Powell.
Title: Searching for geometric finiteness using surface group extensions
Abstract: Farb and Mosher defined convex cocompact subgroups of the mapping class group in analogy with convex cocompact Kleinian groups. These subgroups have since seen immense study and produce surprising applications to the geometry of surface group extension and surface bundles. In particular, Hamenstadt plus Farb and Mosher proved that a subgroup of the mapping class groups is convex cocompact if and only if the corresponding surface group extension is Gromov hyperbolic.
Among Kleinian groups, convex cocompact groups are a special case of the geometrically finite groups. Despite the progress on convex cocompactness, no robust notion of geometric finiteness in the mapping class group has emerged. Durham, Dowdall, Leininger, and Sisto recently proposed that geometric finiteness in MCG(S) might be characterized by the corresponding surface group extension being hierarchically hyperbolic instead of Gromov hyperbolic. We provide evidence in favor of this hypothesis by proving that the surface group extension of the stabilizer of a multicurve is hierarchically hyperbolic.
Valeriano Aiello, Universität Bern, Mathematisches Institut
Title: A reboot of the theory of braids and knots: the Thompson groups as knot constructors
Abstract: In 2014 Vaughan Jones introduced a method to construct knots from elements of the Thompson groups. More precisely, unoriented knots arise from R. Thompson’s group F, while the oriented ones can be produced out of Jones’s oriented Thompson subgroup. This new framework allows one to start a new theory analogous to that of braids and knots, but with the Thompson groups replacing the braid groups. I will report on some work on this project.
Cameron Rudd, University of Illinois UrbanaChampaign
Title: Length, Stable Commutator Length, and Hyperbolic Geometry
Abstract: Geodesic length and stable commutator length give geometric and topological notions of the complexity for nullhomologous elements of the fundamental group of a hyperbolic manifold. The ratio of these complexity measures is a sort of geometrictopological isoperimetric ratio called the stable isoperimetric ratio. In this talk, I will discuss this ratio and mention how it relates to different aspects of the geometry and topology of hyperbolic manifolds. In particular, I will discuss a connection to the spectrum of the Hodge Laplacian.
Roland van der Veen, University of Groningen
Title: Quick quantum invariants of rotational tangles (handout)
Abstract: We introduce a language of tangles that is sufficiently rich to express interesting properties of knots yet rigid enough to satisfy all the axioms found in quantum groups. Examples of such properties are genus, ribbonness, and being a Whitehead double. Mapping the tangles to tensors in a chosen quantum group in a structure preserving way we get a knot invariant sensitive to the properties we are interested in. In favorable cases these invariants can be calculated efficiently using generating function techniques, making this a useful toolbox for lowdimensional topology. Time permitting we will illustrate our technique with an example related to the (colored) Jones polynomials. This is joint work with Dror BarNatan, see our preprint: https://arxiv.org/abs/2109.
Abstract: I will talk about joint work with Andrew Lobb related to Toeplitz's square peg problem, which asks whether every (continuous) Jordan curve in the Euclidean plane contains the vertices of a square. Specifically, we proved that every smooth Jordan curve contains the vertices of a cyclic quadrilateral of any similarity class. I will describe the context for the result and its proof, which involves symplectic geometry in a surprising way.
Other relevant information.
Previous semesters:
Spring 2021, Fall 2020, Spring 2020, Fall 2019, Spring 2019, Fall 2018, Spring 2018, Fall 2017, Spring 2017, Fall 2016, Spring 2016, Fall 2015, Spring 2015, Fall 2014, Spring 2014, Fall 2013, Spring 2013, Fall 2012, Spring 2012, Fall 2011, 2010/11, Spring 2010, Fall 2009, Spring 2009, Fall 2008, Spring 2008, Fall 2007, Spring 2007, Fall 2006.Other area seminars.
 Columbia Symplectic Geometry/Gauge Theory Seminar
 All Columbia Math Dept Seminars
 CUNY Geometry and Topology Seminar
 CUNY Complex Analysis & Dynamics Seminar
 CUNY Magnus Seminar
 Princeton Topology Seminar.