The mapping class group of connect sums of S^2 x S^1

Tara Brendle (University of Glasgow)

Monday 19th October, 2020 16:00-17:00 Online


Let M_n denote the connect sum of n copies of S^2 x S^1.  Laudenbach showed that the mapping class group Mod(M_n) is an extension of the group Out(F_n) by (Z/2)^n, where the latter group is the `sphere twist’ subgroup of Mod(M_n).  In joint work with N. Broaddus and A. Putman, we have shown that in fact this extension splits.  In this talk, we will describe the splitting and discuss some simplifications of Laudenbach’s original proof that arise from our techniques.

The talk will be preceded by a 30 minute tea time. The Zoom link for the seminar is and the passcode is the genus of the two-dimensional sphere (4 letters).

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