Monday 28 July 2025
16:00–17:30*

Anderson Vera (Universidad Nacional de Colombia) — Double lower central series and a double Johnson filtration for the Goeritz group of the sphere

For a triple (K,X,Y) consisting of a group K and two normal subgroups X and Y of K, we introduce a double-indexed family of normal subgroups of K which we call the double lower central series. In particular, if K=XY we show that this family allows us to recover the lower central series of K. If G is a group acting on K preserving X and Y, we show that the double lower central series induces a double-indexed filtration of G. We apply this theory to the group of isotopy classes of self-homeomorphisms of the 3-sphere S^3 which preserves the standard decomposition of S^3 as the gluing of two handlebodies. (Joint work with Kazuo Habiro.)

* Eastern European Time, i.e. UTC+2 in winter and UTC+3 in summer.