This week's seminars
Geometry and Topology Seminar: Dynamical and cohomological obstruction to extending group actions
8 November 2018 13:00 in CM301
For any 3-manifold M with torus boundary, we find finitely generated subgroups of Diff_0(\partial M) whose actions do not extend to actions on M; in many cases there is even no action by homeomorphisms. The obstructions are both dynamical and cohomological in nature. We also show that, if \partial M = S^2, there is no section of the map Diff_0(M) \to \Diff_0(\partial M). This answers a question of Ghys for particular manifolds; and gives tools for progress on the the general program of bordism of group actions. This is joint work with Kathryn Mann.
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