Ancient solutions to free boundary mean curvature flow
Theodora Bourni, Giada Franz
TL;DR
This work studies ancient solutions to the free boundary mean curvature flow in manifolds with convex boundary, focusing on how unstable free boundary minimal hypersurfaces seed rigid ancient flows. Using a Morse-theoretic framework and a detailed linearization around a free boundary minimal hypersurface $\Sigma$, the authors construct an $I$-parameter family of ancient flows when $\Sigma$ has Morse index $I$, and show that all ancient solutions with exponential backward convergence to $\Sigma$ arise from this family. They also provide a second, more geometric construction of mean-convex ancient solutions via a free boundary mean-convex foliation built with an implicit-function theorem and barriers, giving a refined geometric description. Overall, the paper achieves a rigorous classification and rigidity theory for ancient solutions near free boundary minimal hypersurfaces in the convex-boundary setting, illuminating the structure of singularity-formation scenarios in free boundary MCF.
Abstract
We establish rigidity results for ancient solutions to the free boundary mean curvature flow in manifolds with convex boundary. In particular, we show that any free boundary minimal hypersurface of Morse index I admits an I-parameter family of ancient solutions that emanate from it. Moreover, among ancient solutions that backward converge exponentially fast to the minimal hypersurface, these exhaust all possibilities. Additionally, we construct a smooth free boundary mean convex foliation around an unstable free boundary minimal hypersurface that enables us to provide a more detailed geometric description of mean-convex ancient solutions that backward converge to that minimal surface.
