Generalized Ramsey numbers via conflict-free hypergraph matchings

Abstract

Given graphs $G,H$ and an integer $q\ge 2$, the generalized Ramsey number, denoted $r(G,H,q)$, is the minimum number of colours needed to edge-colour $G$ such that every copy of $H$ receives at least $q$ colours. In this paper, we prove that for a fixed integer $k\ge 3$, we have $r(K_n,C_k,3)=n/(k-2)+o(n)$. This generalises work of Joos and Muybayi, who proved $r(K_n,C_4,3)=n/2+o(n)$. We also provide an upper bound on $r(K_{n,n},C_k,3)$, which generalises a result of Joos and Mubayi that $r(K_{n,n},C_4,3)=2n/3+o(n)$. Both of our results are in fact specific cases of more general theorems concerning families of cycles.