# Turán Densities of Some Hypergraphs Related to K_{k+1}^{k}

journal contribution

posted on 2012-09-12, 00:00 authored by József Balogh, Tom Bohman, Béla Bollobás, Yi ZhaoLet $B_i^{(k)}$ be the $k$-uniform hypergraph whose vertex set is of the form $S\cup T$, where $|S|=i$, $|T|=k-1$, and $S\cap T=\emptyset$, and whose edges are the $k$-subsets of $S\cup T$ that contain either $S$ or $T$. We derive upper and lower bounds for the Turán density of $B_i^{(k)}$ that are close to each other as $k\to\infty$. We also obtain asymptotically tight bounds for the Turán density of several other infinite families of hypergraphs. The constructions that imply the lower bounds are derived from elementary number theory by probabilistic arguments, and the upper bounds follow from some results of de Caen, Sidorenko, and Keevash.