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Friday, March 23, 2018 2:30 pm - 2:30 pm EDT (GMT -04:00)

Triple linking numbers and surface systems

Matthias Nagel, McMaster University

We relate fillability of two link exteriors, and the question when two links admit homeomorphic surface systems to (a refinement of) Milnor’s triple linking numbers. This extends a theorem of Davis-Roth to include also links with non-vanishing linking numbers. This is joint work with C. Davis, P. Orson, and M. Powell.

MC 5403

Friday, April 6, 2018 2:30 pm - 2:30 pm EDT (GMT -04:00)

Examples of Ancient Flows on Bundles

McKenzie Wang, McMaster University

I will report on joint work with Peng Lu on constructing ancient flows on a large class of compact bundles. These examples are of type I and include both collapsed and non-collapsed cases. In special cases, we can also describe the forwards limit of these ancient flow. As a bonus of this work, we also obtain examples of such ancient flows for pseudo-Riemannian metrics.

MC 5403

Friday, September 14, 2018 1:30 pm - 1:30 pm EDT (GMT -04:00)

Mapping class groups, coverings, braids and groupoids

Tyrone Ghaswala, University of Manitoba

Given a finite-sheeted, possibly branched covering space between surfaces, it's natural to ask how the mapping class group of the covering surface relates to the mapping class group of the base surface. In this talk, we will take a journey through this question for surfaces with boundary. It will feature appearances from the fundamental groupoid, the Birman-Hilden theorem, the Burau representation and new embeddings of the braid group in mapping class groups.

This is joint work with Alan McLeay.

MC 5403

Friday, September 21, 2018 1:30 pm - 1:30 pm EDT (GMT -04:00)

Loops with Large Twist Get Short Along Quasi-geodesics in Out(F_n)

Yulan Qing, University of Toronto

We study the behaviour of quasi-geodesics in Out(F_n) equipped with word metric. Given an element \phi in Out(F_n) there are several natural paths connecting the origin to \phi in Out(F_n). We show that these paths are, in general, not quasi-geodesics in Out(F_n).  In fact, we clear up the current misunderstanding about distance estimating in Out(F_n) by showing that there exist points in Out(F_n) where all quasi-geodesics between them backtracks in all of the current Out(F_n) complexes. 

MC 5403