The threshold conjecture for random graphs and critical subgraphs

Let HH be a graph with a color-critical edge ee, meaning that χ(He)<χ(H)\chi(H-e)<\chi(H). For a graph GG, let tH(G)t_H(G) and bH(G)b_H(G) be the maximum values of K|K| over, respectively, HH-free and (χ(H)1)(\chi(H)-1)-partite subgraphs of GG, and set

FH={tH(G)=bH(G)}.\mathcal F_H=\{t_H(G)=b_H(G)\}.

Say that GH\mathcal G_H holds for GG if every edge of GG is color-critical in some copy of HH in GG. For a graph property F\mathcal F, write pc(F)p_c(\mathcal F) for its threshold in Gn,pG_{n,p}. The threshold conjecture. For any HH with a color-critical edge,

pc(FH)=O(pc(GH)).p_c(\mathcal F_H)=O\bigl(p_c(\mathcal G_H)\bigr).

For cliques, this is the corresponding theorem; the threshold for GH\mathcal G_H is known, while the conjectured comparison remains open in general. A stronger asymptotic equivalence pc(FH)pc(GH)p_c(\mathcal F_H)\sim p_c(\mathcal G_H) is also suggested in the source.

Sources & referencesView supporting material

Primary source

Bobby DeMarco and Jeff Kahn, “Turán's Theorem for random graphs”, arXiv:1501.01340 (2015).

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