Existence of short simple separating cycles in random high-genus triangulations

Fix θ(0,1/2)\theta\in(0,1/2) and a sequence (gn)(g_n) such that gn/nθg_n/n\rightarrow\theta. Let T2n,gn\mathbf{T}_{2n,g_n} be a uniform triangulation of genus gng_n with 2n2n faces. A simple separating non-contractible cycle is a simple cycle that is separating and non-contractible. The short simple separating cycle conjecture. For every θ(0,1/2)\theta\in(0,1/2), there exists a constant KK such that, with high probability, T2n,gn\mathbf{T}_{2n,g_n} contains a simple, non-contractible, separating cycle of length less than Klog(n)K\log(n).

The theorem preceding this conjecture proves only logarithmic upper and lower bounds for the unrestricted separating systole. This conjecture would establish a logarithmically short simple separating cycle in the random model, despite the deterministic existence problem remaining open.

Sources & referencesView supporting material

Primary source

Baptiste Louf, “The separating systole and the genus ratio of high genus triangulations”, arXiv:2512.05068 (2025).

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