English

Sharp threshold for the Erd\H{o}s-Ko-Rado theorem

Combinatorics 2022-06-08 v3

Abstract

For positive integers nn and kk with n2k+1n\geq 2k+1, the Kneser graph K(n,k)K(n,k) is the graph with vertex set consisting of all kk-sets of {1,,n}\{1,\dots,n\}, where two kk-sets are adjacent exactly when they are disjoint. The independent sets of K(n,k)K(n,k) are kk-uniform intersecting families, and hence the maximum size independent sets are given by the Erd\H{o}s-Ko-Rado Theorem. Let Kp(n,k)K_p(n,k) be a random spanning subgraph of K(n,k)K(n,k) where each edge is included independently with probability pp. Bollob\'as, Narayanan, and Raigorodskii asked for what pp does Kp(n,k)K_p(n,k) have the same independence number as K(n,k)K(n,k) with high probability. For n=2k+1n=2k+1, we prove a hitting time result, which gives a sharp threshold for this problem at p=3/4p=3/4. Additionally, completing work of Das and Tran and work of Devlin and Kahn, we determine a sharp threshold function for all n>2k+1n>2k+1.

Keywords

Cite

@article{arxiv.2105.02985,
  title  = {Sharp threshold for the Erd\H{o}s-Ko-Rado theorem},
  author = {József Balogh and Robert A. Krueger and Haoran Luo},
  journal= {arXiv preprint arXiv:2105.02985},
  year   = {2022}
}

Comments

27 pages; slightly revised with new references; updated funding information; to appear in Random Structures & Algorithms

R2 v1 2026-06-24T01:51:36.143Z