Dear all,
The Groups, Geometry, and Topology (GGT) seminar will take place twice(!) this week:
—Wednesday at 3pm; details below. There will also be a short pre-talk at 2.15 by the speaker in the same room.
—Thursday at 11am; details below.
Wednesday’s talk:
Speaker: Tara Brendle
Location: 40 George Square, LG.08
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Title: The kernel of the Birman-Craggs-Johnson homomorphism
Abstract: The Torelli group is the subgroup of the mapping class group of a surface that acts trivially on the first homology group of that surface. In the 1980s, Dennis Johnson wrote a series of groundbreaking papers describing the structure of this group, culminating in the calculation of its abelianization. The Birman-Craggs Johnson homomorphism measures the 2-torsion part of this abelianization, via certain 3- and 4-manifold invariants. In this talk, we will describe a simple generating set for the kernel of the Birman--Craggs--Johnson homomorphism, which can then be used to give a new and simpler proof of Johnson's calculation of the abelianization of the Torelli group. We will also describe a new method of Minahan-Putman for finding “presentations of representations” that can be used in this setting. This is joint work in progress with Andrew Putman.
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Thursday’s talk:
Speaker: Indira Chatterji
Location: CMT01
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Title: Sidki doubles
Abstract: Given a finitely generated group G, Sidki defined a double X(G) by taking the free product of two copies of G and forcing each element in one copy of G to commute with itself in the other copy. After explaining basic results on this notion of double, I will explain why the double of a
