English

Off-diagonal Ramsey numbers for slowly growing hypergraphs

Combinatorics 2024-09-04 v1

Abstract

For a kk-uniform hypergraph FF and a positive integer nn, the Ramsey number r(F,n)r(F,n) denotes the minimum NN such that every NN-vertex FF-free kk-uniform hypergraph contains an independent set of nn vertices. A hypergraph is slowly growing\textit{slowly growing} if there is an ordering e1,e2,,ete_1,e_2,\dots,e_t of its edges such that eij=1i1ej1|e_i \setminus \bigcup_{j = 1}^{i - 1}e_j| \leq 1 for each i{2,,t}i \in \{2, \ldots, t\}. We prove that if k3k \geq 3 is fixed and FF is any non kk-partite slowly growing kk-uniform hypergraph, then for n2n\ge2, r(F,n)=Ω(nk(logn)2k2). r(F,n) = \Omega\Bigl(\frac{n^k}{(\log n)^{2k - 2}}\Bigr). In particular, we deduce that the off-diagonal Ramsey number r(F5,n)r(F_5,n) is of order n3/\mboxpolylog(n)n^{3}/\mbox{polylog}(n), where F5F_5 is the triple system {123,124,345}\{123, 124, 345\}. This is the only 3-uniform Berge triangle for which the polynomial power of its off-diagonal Ramsey number was not previously known. Our constructions use pseudorandom graphs, martingales, and hypergraph containers.

Keywords

Cite

@article{arxiv.2409.01442,
  title  = {Off-diagonal Ramsey numbers for slowly growing hypergraphs},
  author = {Sam Mattheus and Dhruv Mubayi and Jiaxi Nie and Jacques Verstraëte},
  journal= {arXiv preprint arXiv:2409.01442},
  year   = {2024}
}

Comments

11 pages, 2 figures

R2 v1 2026-06-28T18:31:54.609Z