Columbia Geometric Topology Seminar

Fall 2021


Click here for the Zoom link.

Organizers: Kyle Hayden, Siddhi Krishna
The GT seminar typically meets on Fridays at 2:00pm Eastern time via the Zoom link above. (The password is `math'). 

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Fall 2021

Date Time (Eastern) Speaker Title

September 17

11 am  (Note nonstandard time)

Wenyuan Yang

Proper actions of 3-manifold groups on finite product of quasi-trees

September 24

2 pm

Isaac Sundberg

The Khovanov homology of slice disks

October 1

2 pm

Gage Martin


October 8

2 pm

Joshua Howie


October 15

2 pm

Marissa Loving


October 22

2 pm

Jonathan Zung


October 29




November 5




November 12


Valeriano Aiello


November 19

2 pm

Cameron Rudd


December 3




December 10





Wenyuan Yang, Peking University

September 17, 2021

Title: Proper actions of 3-manifold groups on finite product of quasi-trees 

Abstract: Let M be a compact, connected, orientable 3-manifold. In this talk, I will study when the fundamental group of M acts properly on a finite product of quasi-trees. 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 quasi-isometric embedding of $\pi_1(M)$. This is called property (QT) by Bestvina-Bromberg-Fujiwara, 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 Croke-Kleiner admissible groups and of  relatively hyperbolic groups under natural assumptions. Accordingly, this yields that graph 3-manifold and mixed 3-manifold groups have property (QT). This represents joint work with N.T. Nguyen and S.Z. Han.

Isaac Sundberg, Bryn Mawr College

September 24, 2021

Title: The Khovanov homology of slice disks 

Abstract: A smooth, oriented surface that is properly embedded in the 4-ball can be regarded as a cobordism between the links it bounds, namely, the empty link and its boundary in the 3-sphere. 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 boundary-preserving 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 4-ball. This reflects joint work with Jonah Swann and, separately, with Kyle Hayden.

Gage Martin, Boston College

October 1, 2021



Joshua Howie, UC Davis

October 8, 2021



Marissa Loving, Georgia Tech

October 15, 2021



Jonathan Zung, Princeton University

October 22, 2021



Valeriano AielloUniversität Bern, Mathematisches Institut

November 12, 2021



Cameron Rudd, University of Illinois Urbana-Champaign

November 19, 2021



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Previous semesters:

Spring 2021, Fall 2020Spring 2020Fall 2019Spring 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.

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