Nearly tight bounds for MaxCut in hypergraphs
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866918196858060800 |
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| author | Janzer, Oliver Portier, Julien |
| author_facet | Janzer, Oliver Portier, Julien |
| contents | An $r$-cut of a $k$-uniform hypergraph is a partition of its vertex set into $r$ parts, and the size of the cut is the number of edges which have at least one vertex in each part. The study of the possible size of the largest $r$-cut in a $k$-uniform hypergraph was initiated by Erdős and Kleitman in 1968. For graphs, a celebrated result of Edwards states that every $m$-edge graph has a $2$-cut of size $m/2+Ω(m^{1/2})$, which is sharp. In other words, there exists a cut which exceeds the expected size of a random cut by the order of $m^{1/2}$. Conlon, Fox, Kwan and Sudakov proved that any $k$-uniform hypergraph with $m$ edges has an $r$-cut whose size is $Ω(m^{5/9})$ larger than the expected size of a random $r$-cut, provided that $k \geq 4$ or $r \geq 3$. They further conjectured that this can be improved to $Ω(m^{2/3})$, which would be sharp. Recently, Räty and Tomon improved the bound $m^{5/9}$ to $m^{3/5-o(1)}$ when $r \in \{ k-1,k\}$.
Using a novel approach, we prove the following approximate version of the Conlon-Fox-Kwan-Sudakov conjecture: for each $\varepsilon>0$, there is some $k_0=k_0(\varepsilon)$ such that for all $k>k_0$ and $2\leq r\leq k$, in every $k$-uniform hypergraph with $m$ edges there exists an $r$-cut exceeding the random one by $Ω(m^{2/3-\varepsilon})$. Moreover, we show that (if $k\geq 4$ or $r\geq 3$) every $k$-uniform linear hypergraph has an $r$-cut exceeding the random one by $Ω(m^{3/4})$, which is tight and proves a conjecture of Räty and Tomon. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_08501 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Nearly tight bounds for MaxCut in hypergraphs Janzer, Oliver Portier, Julien Combinatorics An $r$-cut of a $k$-uniform hypergraph is a partition of its vertex set into $r$ parts, and the size of the cut is the number of edges which have at least one vertex in each part. The study of the possible size of the largest $r$-cut in a $k$-uniform hypergraph was initiated by Erdős and Kleitman in 1968. For graphs, a celebrated result of Edwards states that every $m$-edge graph has a $2$-cut of size $m/2+Ω(m^{1/2})$, which is sharp. In other words, there exists a cut which exceeds the expected size of a random cut by the order of $m^{1/2}$. Conlon, Fox, Kwan and Sudakov proved that any $k$-uniform hypergraph with $m$ edges has an $r$-cut whose size is $Ω(m^{5/9})$ larger than the expected size of a random $r$-cut, provided that $k \geq 4$ or $r \geq 3$. They further conjectured that this can be improved to $Ω(m^{2/3})$, which would be sharp. Recently, Räty and Tomon improved the bound $m^{5/9}$ to $m^{3/5-o(1)}$ when $r \in \{ k-1,k\}$. Using a novel approach, we prove the following approximate version of the Conlon-Fox-Kwan-Sudakov conjecture: for each $\varepsilon>0$, there is some $k_0=k_0(\varepsilon)$ such that for all $k>k_0$ and $2\leq r\leq k$, in every $k$-uniform hypergraph with $m$ edges there exists an $r$-cut exceeding the random one by $Ω(m^{2/3-\varepsilon})$. Moreover, we show that (if $k\geq 4$ or $r\geq 3$) every $k$-uniform linear hypergraph has an $r$-cut exceeding the random one by $Ω(m^{3/4})$, which is tight and proves a conjecture of Räty and Tomon. |
| title | Nearly tight bounds for MaxCut in hypergraphs |
| topic | Combinatorics |
| url | https://arxiv.org/abs/2511.08501 |