The atomic structure of ancient grain boundaries

The atomic structure of ancient grain boundaries

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Mat Langford, University of Tennessee at Knoxville

Zoom link: https://princeton.zoom.us/j/99986635712

I will present a series of far-reaching new existence and structure results for convex ancient solutions to mean curvature flow. An interesting picture (conjectured by Huisken and Sinestrari) emerges: convex ancient and translating solutions in slab regions decompose into certain canonical configurations of Grim Reapers, subject to certain necessary constraints. In particular, we construct new families of solutions with discrete symmetries as well as families of solutions which possess only a single reflection symmetry. These include many eternal solutions which do not evolve by translation (resolving a conjecture of White in the negative). Prior to these results, the only known examples were the rotationally symmetric ancient pancake and the rotationally symmetric flying wing translators. Several interesting questions remain open, however. This is joint work with Theodora Bourni and Giuseppe Tinaglia.