English

Ramsey simplicity of random graphs

Combinatorics 2025-03-05 v1

Abstract

A graph GG is qq-Ramsey for another graph HH if in any qq-edge-colouring of GG there is a monochromatic copy of HH, and the classic Ramsey problem asks for the minimum number of vertices in such a graph. This was broadened in the seminal work of Burr, Erd\H{o}s, and Lov\'asz to the investigation of other extremal parameters of Ramsey graphs, including the minimum degree. It is not hard to see that if GG is minimally qq-Ramsey for HH we must have δ(G)q(δ(H)1)+1\delta(G) \ge q(\delta(H) - 1) + 1, and we say that a graph HH is qq-Ramsey simple if this bound can be attained. Grinshpun showed that this is typical of rather sparse graphs, proving that the random graph G(n,p)G(n,p) is almost surely 22-Ramsey simple when lognnpn2/3\frac{\log n}{n} \ll p \ll n^{-2/3}. In this paper, we explore this question further, asking for which pairs p=p(n)p = p(n) and q=q(n,p)q = q(n,p) we can expect G(n,p)G(n,p) to be qq-Ramsey simple. We resolve the problem for a wide range of values of pp and qq; in particular, we uncover some interesting behaviour when n2/3pn1/2n^{-2/3} \ll p \ll n^{-1/2}.

Keywords

Cite

@article{arxiv.2109.04140,
  title  = {Ramsey simplicity of random graphs},
  author = {Simona Boyadzhiyska and Dennis Clemens and Shagnik Das and Pranshu Gupta},
  journal= {arXiv preprint arXiv:2109.04140},
  year   = {2025}
}

Comments

29 pages, 2 figures

R2 v1 2026-06-24T05:49:05.923Z