Ewain Gwynne - Directed distances in bipolar-oriented triangulations: exact exponent & scaling limit
Presenter
January 29, 2026
Abstract
Recorded 29 January 2026. Ewain Gwynne of the University of Chicago presents "Directed distances in bipolar-oriented triangulations: exact exponent and scaling limits" at IPAM's New Interactions Between Probability and Geometry Workshop.
Abstract: We study longest and shortest directed paths in the following natural model of directed random planar maps: the uniform infinite bipolar-oriented triangulation (UIBOT), which is the local limit of uniform bipolar-oriented triangulations around a typical edge.
We construct the Busemann function which measures directed distance to ∞
along a natural interface in the UIBOT. We show that in the case of longest (resp. shortest) directed paths, this Busemann function converges in the scaling limit to a 2/3
-stable Lévy process (resp. a 4/3
-stable Lévy process).
We also prove up-to-constants bounds for directed distances in finite bipolar-oriented triangulations sampled from a Boltzmann distribution, and for size-n
cells in the UIBOT. These bounds imply that in a typical subset of the UIBOT with n
edges, longest directed path lengths are of order n3/4
and shortest directed path lengths are of order n3/8
. These results give the scaling dimensions for discretizations of the (hypothetical) 4/3−−−√
-directed Liouville quantum gravity metrics.
We expect that our techniques can also be applied to prove similar results for directed distances in other random planar map models and for longest increasing subsequences in pattern-avoiding permutations.
Based on joint work with Jacopo Borga.
Learn more online at: https://www.ipam.ucla.edu/programs/workshops/new-interactions-between-probability-and-geometry/?tab=overview