Quasimorphisms on groups of diffeomorphisms

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• Richard Webb, Cambridge
• Wednesday 20 November 2019, 16:00-17:00
• MR13.

If you have a question about this talk, please contact Ivan Smith.

I will explain how to construct an unbounded quasimorphism on the group of isotopically-trivial diffeomorphisms of a surface of genus at least two. As a corollary the commutator length and fragmentation norm are both (stably) unbounded, which solves an open problem of Burago—Ivanov—Polterovich. I will provide some background about these groups before introducing new geometric tools to study them. This is joint work with Jonathan Bowden and Sebastian Hensel.

This talk is part of the Differential Geometry and Topology Seminar series.

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