t-Wise Berge and t-Heavy Hypergraphs

Gerbner, Dániel and Nagy, Dániel and Patkós, Balázs and Vizer, Máté (2020) t-Wise Berge and t-Heavy Hypergraphs. SIAM JOURNAL ON DISCRETE MATHEMATICS, 34 (3). pp. 1813-1829. ISSN 0895-4801

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Abstract

In many proofs concerning extremal parameters of Berge hypergraphs one starts with analyzing that part of that shadow graph which is contained in many hyperedges. Capturing this phenomenon we introduce two new types of hypergraphs. A hypergraph ${\mathcal H}$ is a $t$-heavy copy of a graph $F$ if there is a copy of $F$ on its vertex set such that each edge of $F$ is contained in at least $t$ hyperedges of ${\mathcal H}$. ${\mathcal H}$ is a $t$-wise Berge copy of $F$ if additionally for distinct edges of $F$ those $t$ hyperedges are distinct. We extend known upper bounds on the Turán number of Berge hypergraphs to the $t$-wise Berge hypergraphs case. We asymptotically determine the Turán number of $t$-heavy and $t$-wise Berge copies of long paths and cycles and exactly determine the Turán number of $t$-heavy and $t$-wise Berge copies of cliques. In the case of 3-uniform hypergraphs, we consider the problem in more details and obtain additional results.

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