English

Ramsey goodness of bounded degree trees

Combinatorics 2016-11-09 v1

Abstract

Given a pair of graphs GG and HH, the Ramsey number R(G,H)R(G,H) is the smallest NN such that every red-blue coloring of the edges of the complete graph KNK_N contains a red copy of GG or a blue copy of HH. If a graph GG is connected, it is well known and easy to show that R(G,H)(G1)(χ(H)1)+σ(H)R(G,H) \geq (|G|-1)(\chi(H)-1)+\sigma(H), where χ(H)\chi(H) is the chromatic number of HH and σ(H)\sigma(H) is the size of the smallest color class in a χ(H)\chi(H)-coloring of HH. A graph GG is called HH-good if R(G,H)=(G1)(χ(H)1)+σ(H)R(G,H)= (|G|-1)(\chi(H)-1)+\sigma(H). The notion of Ramsey goodness was introduced by Burr and Erd\H{o}s in 1983 and has been extensively studied since then. In this paper we show that if nΩ(Hlog4H)n\geq \Omega(|H| \log^4 |H|) then every nn-vertex bounded degree tree TT is HH-good. The dependency between nn and H|H| is tight up to log\log factors. This substantially improves a result of Erd\H{o}s, Faudree, Rousseau, and Schelp from 1985, who proved that nn-vertex bounded degree trees are HH-good when when nΩ(H4)n \geq \Omega(|H|^4).

Keywords

Cite

@article{arxiv.1611.02688,
  title  = {Ramsey goodness of bounded degree trees},
  author = {Igor Balla and Alexey Pokrovskiy and Benny Sudakov},
  journal= {arXiv preprint arXiv:1611.02688},
  year   = {2016}
}