Ore-degree conditions for matchings in uniform hypergraphs

Abstract

Let $σ_r(\mathcal{H})$ be the minimum sum of vertex degrees over all nonedges of an $r$-uniform hypergraph $\mathcal{H}$ on $n$ vertices. Balogh, Palmer and Raeisi conjectured that $n>2rs$ and $σ_r(\mathcal{H})>r[\binom{n-1}{r-1}-\binom{n-s}{r-1}]$ imply the existence of a matching of size $s$ in $\mathcal{H}$. We prove that, for every fixed $r\ge3$ and all sufficiently large $s$, $σ_r(\mathcal{H})>r[\binom{n-1}{r-1}-\binom{n-s}{r-1}]$ forces an $s$-matching whenever $n\ge rs+\lfloor(r-1)^{r-1}/r^{r-2}\rfloor$. A complete $r$-graph on $rs-1$ vertices together with $\lfloor(r-1)^{r-1}/r^{r-2}\rfloor$ isolated vertices shows that the vertex bound is sharp for all sufficiently large $s$. By adding new vertices to $\mathcal{H}$, retaining all its edges, and adding every $r$-set containing at least one new vertex as an edge, we also deduce that $n\ge rs+C$ suffices under the same degree condition for every $s\ge1$, where $C$ is a finite constant depending only on $r$. For $r=3$, we provide the explicit sufficient order $n\ge\lceil(7s+11)/2\rceil$ for $s\ge6$, together with bounds for $2\le s\le5$, establishing the conjecture in this uniformity. For $s=2$, we improve the known sufficient order $2r+2$ to $2r+1$ for every $r\ge3$ and show that this order is best possible.