Sharp bounds for rainbow matchings in hypergraphs

Abstract

Suppose we are given matchings $M_1,....,M_N$ of size $t$ in some $r$-uniform hypergraph, and let us think of each matching having a different color. How large does $N$ need to be (in terms of $t$ and $r$) such that we can always find a rainbow matching of size $t$? This problem was first introduced by Aharoni and Berger, and has since been studied by several different authors. For example, Alon discovered an intriguing connection with the Erdős--Ginzburg--Ziv problem from additive combinatorics, which implies certain lower bounds for $N$. For any fixed uniformity $r\ge 3$, we answer this problem up to constant factors depending on $r$, showing that the answer is on the order of $t^r$. Furthermore, for any fixed $t$ and large $r$, we determine the answer up to lower order factors. We also prove analogous results in the setting where the underlying hypergraph is assumed to be $r$-partite. Our results settle questions of Alon and of Glebov-Sudakov-Szabó.