English

Ordered Ramsey numbers of powers of paths

Combinatorics 2024-01-12 v2

Abstract

Given two vertex-ordered graphs GG and HH, the ordered Ramsey number R<(G,H)R_<(G,H) is the smallest NN such that whenever the edges of a vertex-ordered complete graph KNK_N are red/blue-coloured, then there is a red (ordered) copy of GG or a blue (ordered) copy of HH. Let PntP_n^t denote the tt-th power of a monotone path on nn vertices. The ordered Ramsey numbers of powers of paths have been extensively studied. We prove that there exists an absolute constant CC such that R<(Ks,Pnt)R(Ks,Kt)CnR_<(K_s,P_n^t)\leq R(K_s,K_t)^{C} \cdot n holds for all s,t,ns,t,n, which is tight up to the value of CC. As a corollary, we obtain that there is an absolute constant CC such that R<(Kn,Pnt)nCtR_<(K_n,P_n^t)\leq n^{Ct}. These results resolve a problem and a conjecture of Gishboliner, Jin and Sudakov. Furthermore, we show that R<(Pnt,Pnt)n4+o(1)R_<(P_n^t,P_n^t)\leq n^{4+o(1)} for any fixed tt. This answers questions of Balko, Cibulka, Kr\'al and Kyn\v{c}l, and of Gishboliner, Jin and Sudakov.

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Cite

@article{arxiv.2401.02360,
  title  = {Ordered Ramsey numbers of powers of paths},
  author = {António Girão and Barnabás Janzer and Oliver Janzer},
  journal= {arXiv preprint arXiv:2401.02360},
  year   = {2024}
}

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12 pages