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

January 28 
2pm Eastern 
Oliver Singh 
Pseudoisotopies and diffeomorphisms of 4manifolds 
February 4 
2pm Eastern 
Markov chains on groups and quasiisometries 

February 11 
2pm Eastern  Allison N. Miller 
Slicing knots in definite 4manifolds 
February 18 
2pm Eastern 
Lspaces, taut foliations and the Whitehead link 

March 4 
2pm Eastern 
Counterexamples in 4manifold topology 

March 11 
2pm Eastern 
Taut foliations of 3manifolds with Heegaard genus two 

March 25 
2pm Eastern 
Oyku Yurttas 
Curves, braids and crosscap transpositions 
April 1 
2pm Eastern 
Equivariant knots and knot Floer homology  
April 1 
4:30pm Eastern (Special Bonus Seminar!) Mathematics Hall, Room 312 (inperson) 
Special Lagrangians from the perspective of Morse theory  
April 5 
12pm Eastern (Special Bonus Seminar!) Uris Hall, Room 331 (inperson) 
Marithania Silvero  Khovanov homology of 4braids in polynomial time 
April 5 
1pm Eastern (Special Bonus Seminar!) Uris Hall, Room 331 (inperson) 
Józef Henryk Przytycki  Khovanov homology of 4braids in polynomial time: Independence complexes of circle graphs 
April 8 
2pm Eastern 
Hermitian Lie groups as symplectic groups over noncommutative algebras 

April 15 
2pm Eastern  "Representations are sheaves" for Legendrian 2weaves  
April 22  2pm Eastern  Feride Ceren Köse  On the amphichirality of symmetric unions 
April 22 
4:45pm Eastern (Special Bonus Seminar!) Room TBD (inperson) 
Marco Golla  Symplectic fillings of divisorial contact structures 
April 29  2pm Eastern  Alexandra Edletzberger  QuasiIsometries for certain RightAngled Coxeter groups 
Abstracts
Oliver Singh
Title: Pseudoisotopies and diffeomorphisms of 4manifolds
Abstract: I will talk about pseudoisotopy, a notion important for understanding selfdiffeomorphisms of manifolds up to isotopy. Pseudoisotopies of manifolds in dimensions 5 and up were understood in the 70s by work of Cerf for simply connected manifolds, and by Hatcher and Wagoner in the nonsimply connected case, using invariants from algebraic Ktheory. Quinn later proved Cerf’s result topologically in dimension 4, leading to a classification of selfhomeomorphisms of simply connected 4manifolds up to isotopy. I will talk about my work on what Hatcher and Wagoner’s Ktheoretic invariants can say about pseudoisotopies of nonsimply connected 4manifolds, and how they can be used to construct diffeomorphisms of certain 4manifolds which are pseudoisotopic but not isotopic to the identity.
Alessandro Sisto
Title: Markov chains on groups and quasiisometries
Abstract: Random walks on groups provide a model for a "generic" element of a group, and they're very interesting and very wellstudied. In geometric group theory it is natural to consider quasiisometric groups, but unfortunately random walks are not compatible with quasiisometries, in the sense that they cannot be "pushed forward" via quasiisometries in any meaningful sense. To resolve this, in this talk I will propose the study of more general Markov processes on groups that are indeed "quasiisometry compatible", and present the first results about them. In particular, I will discuss a central limit theorem for random walks whose proof exploits this perspective of pushing forward Markov chains.
Based on joint work with Antoine Goldsborough.
Allison N. Miller
Title: Slicing knots in definite 4manifolds
Abstract: A knot is called "slice" if it bounds an embedded disc in the 4ball. A natural extension of this idea is to think about knots that bound embedded discs in other simple 4manifolds. We'll talk about some constructions and obstructions in the specific case of connected sums of the complex projective plane. Tools include Donaldson's theorem on the intersection form of smooth definite 4manifolds and Freedman's result that knots with trivial Alexander polynomial are topologically slice.
Diego Santoro
Title: Lspaces, taut foliations and the Whitehead link
Abstract: The Lspace conjecture predicts strong connections among properties relating the Heegaard Floer homology, foliations and the fundamental group of an irreducible rational homology 3sphere. I will introduce this conjecture and present some results concerning the structure of the set of the Lspace surgery slopes for links with unknotted components and linking number zero. For what concerns foliations, I will discuss the existence of taut foliations on the Dehn fillings of some kholed torus bundles over the circle. These results will be used to study the Lspace conjecture for the rational homology spheres arising as Dehn surgery on the Whitehead link.
Arunima Ray
Title: Counterexamples in 4manifold topology
Abstract: I will discuss the relationships among a variety of equivalence relations on 4manifolds, such as diffeomorphism, homeomorphism, hcobordism, and homotopy equivalence, with the goal of organising a zoo of counterexamples and discovering unanswered questions. There will be a flowchart and a table. The talk is based on an upcoming, partly survey paper with Daniel Kasprowski and Mark Powell.
Tao Li
Title: Taut foliations of 3manifolds with Heegaard genus two
Abstract: Let M be a closed, orientable, and irreducible 3manifold with Heegaard genus two. We prove that if the fundamental group of M is leftorderable then M admits a coorientable taut foliation.
Oyku Yurttas
Title: Curves, braids and crosscap transpositions
Abstract: Multicurves (systems of mutually disjoint essential simple closed curves) have played a central role in the study of mapping class groups of surfaces since the work of Dehn. Such systems are usually described combinatorially using techniques such as the DehnThurston coordinate system or train tracks. In the case where the surface is an npunctured disk D_n multicurves are beautifully described by their Dynnikov coordinates, a collection of 2n4 linear combinations of intersection numbers with the 3n5 edges of a neartriangulation of D_n. The Mapping Class Group of D_n is canonically isomorphic to Artin's braid group modulo its center. The action of Artin's braid generators on the set of Dynnikov coordinates is given by socalled update rules. In this talk we survey Dynnikov coordinates and update rules, and then provide natural analogues of these tools for an npunctured nonorientable surface N_{k,n} of genus k. Namely, we introduce generalized Dynnikov coordinates for multicurves in N_{k,n}, and then describe the action of crosscap transpositions in terms of these coordinates.
Irving Dai
Title: Equivariant knots and knot Floer homology
Abstract: We define several equivariant concordance invariants using knot Floer homology. We show that our invariants provide a lower bound for the equivariant slice genus and use this to give a family of strongly invertible slice knots whose equivariant slice genus grows arbitrarily large, answering a question of Boyle and Issa. We also apply our formalism to several seemingly nonequivariant questions. In particular, we show that knot Floer homology can be used to detect exotic pairs of slice disks, recovering an example due to Hayden. This is joint work with Abhishek Mallick and Matthew Stoffregen.
Emily Windes
Title: Special Lagrangians from the perspective of Morse theory
Abstract: In this talk, we consider a Lagrange multipliers problem where the constraint is a section of a bundle E>M. We relate the Morse homology of a function restricted to the zero set of the section to the Morse homology of the associated Lagrange function on the total space E^*. Then we discuss a similar, infinitedimensional Lagrange multipliers problem appearing in Donaldson and Segal’s paper "Gauge Theory in Higher Dimensions II". The long term goal is to apply Floer theory to a functional whose critical points are a generalization of threedimensional, special Lagrangian submanifolds.
Marithania Silvero and Josef Przytycki (Double Header)
Date: April 5th (Bonus seminar at a special time!)
Title: Khovanov homology of 4braids in polynomial time
Abstract: Khovanov homology is a link invariant which generalizes Jones polynomial. In general, computing Jones polynomial (so also Khovanov homology) is NPhard. However, if we consider a closed braid of a fixed number of strands, it is wellknown that all classical quantum invariants (in particular Jones polynomial) can be computed in polynomial time. We conjecture that the complexity of computing Khovanov homology of a closed braid of fixed number of strands is polynomial with respect to the number of crossings.
In this talk we show some advances on the conjecture, showing that the result holds when considering extreme Khovanov homology of closed braids of at most 4 strands. As a consequence, we get an obstruction for a link to have braid index 4 in terms of it extreme Khovanov homology.
Eugen Rogozinnikov
Title: Hermitian Lie groups as symplectic groups over noncommutative algebras
Abstract: In my talk, I introduce the symplectic group $\Sp_2(A,\sigma)$ over a noncommutative algebra $A$ with an antiinvolution $\sigma$ and show that many classical Lie groups can be seen in this way. Of particular interest will be the classical Hermitian Lie groups of tube type and their complexifications. For these groups, I construct different models of the symmetric space in terms of the group $\Sp_2(A,\sigma)$. We obtain generalizations of several models of the hyperbolic plane and the threedimensional hyperbolic space. This is a joint work with D. Alessandrini, A. Berenstein, V. Retakh and A. Wienhard.
Kevin Sackel
Title: "Representations are sheaves" for Legendrian 2weaves
Abstract: Given a trivalent plane graph embedded in the 2sphere, there is a rich algebraic structure which arises from contact geometric considerations. The graph corresponds to a certain associated Legendrian surface via a construction of Treumann and Zaslow. In prior work, Casals and Murphy computed the Legendrian contact dgalgebra for (the Legendrian satellite of) this Legendrian 2weave over commutative coefficients, the group ring of the first homology group. We extend their computation to the noncommutative setting, working over the group ring of the fundamental group. For this family of Legendrian surfaces, we further verify the conjecture that "representations are sheaves," i.e. that the moduli space of representations of this fully noncommutative dgalgebra are in bijective correspondence with a certain moduli space of constructible sheaves. Aside from the contactgeometric story, we will emphasize the extraordinarily combinatorial and computational nature of the algebraic structure one obtains.
Feride Ceren Köse
Title: On the amphichirality of symmetric unions
Abstract: Symmetric unions are an interesting class of knots. Although they have not been studied much for their own sake, they frequently appear in the literature. One such instance regards the question of whether there is a nontrivial knot with trivial Jones polynomial. In my talk, I will describe a class of symmetric unions, constructed by Tanaka, such that if any are amphichiral, they would have trivial Jones polynomial. Then I will show how such a knot not only answers the above question but also gives rise to a counterexample to the Cosmetic Surgery Conjecture. However, I will prove that such a knot is in fact trivial and hence cannot be used to answer any of these questions. If time permits, I will discuss how the arguments that go into this proof can be generalized to study amphichiral symmetric unions.
Marco Golla
Title: Symplectic fillings of divisorial contact structures
Abstract: If a (possibly singular) complex curve in a Kähler surface has positive selfintersection, then it has a standard symplectically concave neighbourhood, and therefore an associated divisorial contact structure. Motivated by the study of singular symplectic curves in the complex projective plane, we will discuss the existence and classification of fillings of some of these contact structures. This is based on joint work with Laura Starkston.
Alexandra Edletzberger
Title: QuasiIsometries for certain RightAngled Coxeter groups
Abstract: In the hunt for a solution to the QuasiIsometry Problem of rightangled Coxeter groups (RACGs), we use a quasiisometry invariant that is obtained by a certain splitting of the groups. In this talk, we introduce this splitting, the socalled Graph of Cylinders, and give its construction for a large family of (in particular nonhyperbolic) RACGs, that can be read off the presentation graph. This means, that we can distinguish certain RACGs up to quasiisometry just by comparing the information their presentation graphs provide. Often, even more is possible: Under one additional assumption, by this comparison RACGs can also be identified as quasiisometric.
Other relevant information.
Previous semesters:
Fall 2021, 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.