Critical maximum-cut conjecture for random triangle-free graphs

From papers

Let T(n,m)\mathcal{T}(n,m) be the set of triangle-free graphs on nn vertices with mm edges, and let a graph drawn uniformly from T(n,m)\mathcal{T}(n,m) be denoted by GG. For a graph GG, a maximum cut is a cut containing the largest possible number of edges. Write whp\operatorname{whp} for “with high probability” and mcn3/2m\sim c n^{3/2} for an edge count asymptotic to cn3/2c n^{3/2}.

Critical maximum-cut conjecture. There exists c>0c^*>0 and a continuous function δ:(c,)(0,1/2]\delta:(c^*,\infty)\to(0,1/2] such that:

if c<c and mcn3/2, then whp G has a maximum cut of size (1/2+o(1))m;\text{if }c<c^*\text{ and }m\sim c n^{3/2},\text{ then whp }G\text{ has a maximum cut of size }(1/2+o(1))m;

and

if c>c and mcn3/2, then whp G has a maximum cut of size (1/2+δ(c)+o(1))m.\text{if }c>c^*\text{ and }m\sim c n^{3/2},\text{ then whp }G\text{ has a maximum cut of size }(1/2+\delta(c)+o(1))m.

This gives a precise proposed order–disorder transition at the scale mn3/2m\sim n^{3/2}: below the critical constant the maximum-cut fraction tends to 1/21/2, while above it the fraction is separated from 1/21/2 by the positive quantity δ(c)\delta(c). The source presents this as a conjecture and does not provide a resolution.

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Sources & referencesView supporting material

Primary source

Matthew Jenssen, Will Perkins and Aditya Potukuchi, “On the evolution of structure in triangle-free graphs”, arXiv:2312.09202 (2025).

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