Tue, April 7, 2026
1:50 pm - 2:50 pm
Enarson Classroom Building 354
Corey Bregman
Tufts University
Title
Diffeomorphism groups of reducible 3-manifolds
Abstract
Geometrization is a powerful principle which has shaped our understanding of irreducible 3-manifolds and, more recently, the structure of their diffeomorphism groups. However, diffeomorphism groups of reducible 3-manifolds remain somewhat elusive. In this talk we survey some recent results in this direction, using the action of the diffeomorphism group on a space of separating systems, a topological poset parametrizing all collections of embedded spheres which decompose a reducible 3-manifold into its irreducible factors. Our approach provides an effective tool for computation, which we exhibit through various applications. This is joint work with R. Boyd and J. Steinebrunner.