English

On generalized Ramsey numbers in the non-integral regime

Combinatorics 2024-10-16 v3

Abstract

A (p,q)(p,q)-coloring of a graph GG is an edge-coloring of GG such that every pp-clique receives at least qq colors. In 1975, Erd\H{o}s and Shelah introduced the generalized Ramsey number f(n,p,q)f(n,p,q) which is the minimum number of colors needed in a (p,q)(p,q)-coloring of KnK_n. In 1997, Erd\H{o}s and Gy\'arf\'as showed that f(n,p,q)f(n,p,q) is at most a constant times np2(p2)q+1n^{\frac{p-2}{\binom{p}{2} - q + 1}}. Very recently the first author, Dudek, and English improved this bound by a factor of logn1(p2)q+1\log n^{\frac{-1}{\binom{p}{2} - q + 1}} for all qp226p+554q \le \frac{p^2 - 26p + 55}{4}, and they ask if this improvement could hold for a wider range of qq. We answer this in the affirmative for the entire non-integral regime, that is, for all integers p,qp, q with p2p-2 not divisible by (p2)q+1\binom{p}{2} - q + 1. Furthermore, we provide a simultaneous three-way generalization as follows: where pp-clique is replaced by any fixed graph FF (with V(F)2|V(F)|-2 not divisible by E(F)q+1|E(F)| - q + 1); to list coloring; and to kk-uniform hypergraphs. Our results are a new application of the Forbidden Submatching Method of the second and fourth authors.

Keywords

Cite

@article{arxiv.2212.10542,
  title  = {On generalized Ramsey numbers in the non-integral regime},
  author = {Patrick Bennett and Michelle Delcourt and Lina Li and Luke Postle},
  journal= {arXiv preprint arXiv:2212.10542},
  year   = {2024}
}

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10 pages