Independent transversals in hypergraphs with low codegrees

Abstract

We prove that for every fixed $r\geq3$, $k>0$ and $\varepsilon\in(0,1)$, there is $γ>0$ such that the following holds for all sufficiently large $b$. An $r$-uniform hypergraph $\mathcal H$ whose vertex set is partitioned into parts of size at least $b$ contains at least $\lceil(1-\varepsilon)b\rceil$ pairwise vertex-disjoint independent transversals, provided that the average degree in each part is at most $kb^{r-1}$ and maximum $j$-codegree $Δ_j(\mathcal H)\leqγb^{r-j}$ for $2\leq j<r$. Under the same average degree, if $q$ is the minimum part size and $Δ_j(\mathcal H)=o(q^{r-j})$ for $2\leq j<r$, the maximum number of pairwise vertex-disjoint independent transversals is $(1-o(1))q$ as $q\to\infty$. We develop an iterative halving reduction for partitioned hypergraphs to apply the theorem of Delcourt and Postle on matchings avoiding forbidden submatchings.