Topology Seminar

Please note that the list below only shows forthcoming events, which may not include regular events that have not yet been entered for the forthcoming term. Please see the past events page for a list of all seminar series that the department has on offer.

Past events in this series
27 November 2017
15:45
Steven Sivek
Abstract

The cyclic surgery theorem of Culler, Gordon, Luecke, and Shalen implies that any knot in S^3 other than a torus knot has at most two nontrivial cyclic surgeries. In this talk, we investigate the weaker notion of SU(2)-cyclic surgeries on a knot, meaning surgeries whose fundamental groups only admit SU(2) representations with cyclic image. By studying the image of the SU(2) character variety of a knot in the “pillowcase”, we will show that if it has infinitely many SU(2)-cyclic surgeries, then the corresponding slopes (viewed as a subset of RP^1) have a unique limit point, which is a finite, rational number, and that this limit is a boundary slope for the knot. As a corollary, it follows that for any nontrivial knot, the set of SU(2)-cyclic surgery slopes is bounded. This is joint work with Raphael Zentner.

4 December 2017
15:45
Abstract

The bipolar filtration of Cochran, Harvey and Horn initiated the study of deeper structures of the smooth concordance group of the topologically slice knots. We show that the graded quotient of the bipolar filtration has infinite rank at each stage greater than one. To detect nontrivial elements in the quotient, the proof uses higher order amenable Cheeger-Gromov $L^2$ $\rho$-invariants and infinitely many Heegaard Floer correction term $d$-invariants simultaneously. This is joint work with Jae Choon Cha.

22 January 2018
15:45
Constantin Teleman
Abstract

I relate two very classical dualities in quantum field theory: the high/low temperature 
duality in 2D abelian lattice models with the electric-magnetic duality in 3D topological 
electromagnetism. Both of them are categorified versions of the Fourier transform. The 
connection involves the notion of relative field theory and places lattice theories in 
the setting of fully extended TQFTs. This allows one to generalise the dualities to 
non-abelian groups, and even to finite semi-simple Hopf algebras. This is joint work 
with Dan Freed.

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