A “cubist” decomposition of the Handel-Mosher axis bundle & the conjugacy problem for Out(F_r)

Seminar: 
Geometry & Topology
Event time: 
Tuesday, April 15, 2025 - 4:00pm
Location: 
KT 207
Speaker: 
Catherine Pfaff
Speaker affiliation: 
Institute for Advanced Study/Queen's University
Event description: 

Outer automorphisms of free groups are largely studied via their action on Culler-Vogtmann Outer space. However, unlike in hyperbolic space or Teichmuller space (surface) settings, the dynamically minimal (fully irreducible) free group outer automorphisms act on Culler-Vogtmann Outer space with a collection of axes, whose closure is the Handel-Mosher ``axis bundle.'' Not much of the structure of this axis bundle has yet been understood. Together with Chi Cheuk Tsang, we prove that the axis bundle has a "cubist" structure and use this structure to find preferred axes for these outer automorphisms. We then use these axes to provide a solution to the fully irreducible conjugacy problem. This work can be seen as in analogy with that of Hamenstadt and Agol in the surface setting.