English

Hypergraph Turan with bounded matching number

Combinatorics 2026-07-14 v1

Abstract

For a fixed graph GG, an rr-uniform hypergraph is said to contain a Berge-GG if there exists a bijection f ⁣:E(G)E(H)f\colon E(G)\to E(\mathcal{H}) for some subhypergraph H\mathcal{H} such that ef(e)e\subseteq f(e) for every eE(G)e\in E(G). Motivated by Alon and Frankl's study of Tur\'an problems under bounded matching constraints, we investigate the maximum number of edges in rr-uniform Berge-K3K_3-free hypergraphs with matching number at most~ss. We determine the exact Tur\'an numbers for the cases r=3r=3 and r=4r=4. For r=3r=3 and n3sn \geq 3 s, we prove that every nn-vertex Berge- K3K_3-free 3-graph with matching number ss has at most s(n2s)s(n-2 s) edges, and we characterize the unique extremal hypergraph attaining equality. For r=4r=4 and n4sn \geq 4 s, the maximum number of edges is s(n2s)/2s\lfloor(n-2 s) / 2\rfloor, except for the exceptional case s=1s=1 and n1(mod4)n \equiv 1(\bmod 4), in which the bound is (n1)/2(n-1) / 2. As a corollary, our results recover the classical theorem of Gy\H{o}ri on Berge-K3K_3-free hypergraphs.

Cite

@article{arxiv.2607.12300,
  title  = {Hypergraph Turan with bounded matching number},
  author = {Yue Xu and Jiasheng Zeng and Xiao-Dong Zhang},
  journal= {arXiv preprint arXiv:2607.12300},
  year   = {2026}
}

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15 pages