English

All Ramsey critical graphs for a large tree versus $tK_{m}$

Combinatorics 2025-06-24 v1

Abstract

Let H,H1H, H_{1} and H2H_{2} be graphs, and let H(H1,H2)H\rightarrow (H_{1}, H_{2}) denote that any red-blue coloring of E(H)E(H) yields a red copy of H1H_{1} or a blue copy of H2H_{2}. The Ramsey number for H1H_{1} versus H2H_{2}, r(H1,H2)r(H_{1}, H_{2}), is the minimum integer NN such that KN(H1,H2)K_{N}\rightarrow (H_{1}, H_{2}). The Ramsey critical graph HH for H1H_{1} versus H2H_{2} is a red-blue edge-colored KN1K_{N- 1} such that H↛(H1,H2)H\not\rightarrow (H_{1}, H_{2}), where N=r(H1,H2)N= r(H_{1}, H_{2}). In this paper, we characterize all Ramsey critical graphs for a large tree versus tKmtK_{m}. As a corollary, we determine the star-critical Ramsey number for a large tree versus tKmtK_{m}.

Keywords

Cite

@article{arxiv.2506.18235,
  title  = {All Ramsey critical graphs for a large tree versus $tK_{m}$},
  author = {Zhiyu Cheng and Zhidan Luo and Pingge Chen},
  journal= {arXiv preprint arXiv:2506.18235},
  year   = {2025}
}
R2 v1 2026-07-01T03:28:45.052Z