English

Off-diagonal hypergraph Ramsey numbers

Combinatorics 2015-06-01 v2

Abstract

The Ramsey number rk(s,n)r_k(s,n) is the minimum NN such that every red-blue coloring of the kk-subsets of {1,,N}\{1, \ldots, N\} contains a red set of size ss or a blue set of size nn, where a set is red (blue) if all of its kk-subsets are red (blue). A kk-uniform \emph{tight path} of size ss, denoted by PsP_{s}, is a set of ss vertices v1<<vsv_1 < \cdots < v_{s} in Z\mathbb{Z}, and all sk+1s-k+1 edges of the form {vj,vj+1,,vj+k1}\{v_j,v_{j+1},\ldots, v_{j + k -1}\}. Let rk(Ps,n)r_k(P_s, n) be the minimum NN such that every red-blue coloring of the kk-subsets of {1,,N}\{1, \ldots, N\} results in a red PsP_{s} or a blue set of size nn. The problem of estimating both rk(s,n)r_k(s,n) and rk(Ps,n)r_k(P_s, n) for k=2k=2 goes back to the seminal work of Erdos and Szekeres from 1935, while the case k3k\ge 3 was first investigated by Erdos and Rado in 1952. In this paper, we deduce a quantitative relationship between multicolor variants of rk(Ps,n)r_k(P_s, n) and rk(n,n)r_k(n, n). This yields several consequences including the following: (1) We determine the correct tower growth rate for both rk(s,n)r_k(s,n) and rk(Ps,n)r_k(P_s, n) for sk+3s \ge k+3. The question of determining the tower growth rate of rk(s,n)r_k(s,n) for all sk+1s \ge k+1 was posed by Erdos and Hajnal in 1972. (2) We show that determining the tower growth rate of rk(Pk+1,n)r_k(P_{k+1}, n) is equivalent to determining the tower growth rate of rk(n,n)r_k(n,n), which is a notorious conjecture of Erdos, Hajnal and Rado from 1965 that remains open. Some related off-diagonal hypergraph Ramsey problems are also explored.

Keywords

Cite

@article{arxiv.1505.05767,
  title  = {Off-diagonal hypergraph Ramsey numbers},
  author = {Dhruv Mubayi and Andrew Suk},
  journal= {arXiv preprint arXiv:1505.05767},
  year   = {2015}
}
R2 v1 2026-06-22T09:38:50.887Z