# Deep slice knots and Arf invariants

Tuesday, November 24, 2020 10:00 AM

Michael Klug (UC Berkeley / MPIM Bonn)

I will discuss two recent projects - one concerning the existence/nonexistence of so called deep slice knots (knots in the boundary of a 4-manifold that are slice in the 4-manifold but not slice in a collar neighborhood of the boundary), and the other concerning the relationship between various Arf invariants that come up when studying knots in the boundaries of 4-manifolds that bound characteristic surfaces. It will be a calm look back on some of the invariants that existed in low dimensional topology before the advent of gauge theory.