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Sparse hypergraphs: New bounds and constructions
Journal of Combinatorial Theory Series B ( IF 1.2 ) Pub Date : 2020-11-05 , DOI: 10.1016/j.jctb.2020.10.003
Gennian Ge , Chong Shangguan

Let fr(n,v,e) denote the maximum number of edges in an r-uniform hypergraph on n vertices, in which the union of any e distinct edges contains at least v+1 vertices. The study of fr(n,v,e) was initiated by Brown, Erdős and Sós more than forty years ago. In the literature, the following conjecture is well known.

Conjecture: nko(1)<fr(n,er(e1)k+1,e)=o(nk) holds for all fixed integers r>k2 and e3 as n.

For r=3,e=3,k=2, the bound n2o(1)<f3(n,6,3)=o(n2) was proved by the celebrated (6,3)-theorem of Ruzsa and Szemerédi. In this paper, we add more evidence for the validity of the conjecture. On one hand, using the hypergraph removal lemma we show that the upper bound part of the conjecture is true for all fixed integers rk+1e3. On the other hand, using tools from additive number theory we present several constructions showing that the lower bound part of the conjecture is true for r3, k=2 and e=4,5,7,8. Prior to our results, all known constructions that match the conjectured lower bound satisfy either r=3 or e=3. Our constructions are the first ones in the literature that break this barrier.



中文翻译:

稀疏超图:新界限和构造

F[RñvË表示n个顶点上r-一致超图中的最大边数,其中任何e个不同边的并集至少包含v+1个顶点。研究F[RñvË四十多年前由布朗,埃德斯和索斯发起。在文献中,以下推测是众所周知的。

推测: ñķ-Ø1个<F[RñË[R-Ë-1个ķ+1个Ë=Øñķ 适用于所有固定整数 [R>ķ2Ë3ñ

对于 [R=3Ë=3ķ=2,界限 ñ2-Ø1个<F3ñ63=Øñ2Ruzsa和Szemerédi的著名(6,3)定理证明了这一点。在本文中,我们为猜想的有效性添加了更多证据。一方面,使用超图去除引理,我们证明了猜想的上限对所有固定整数都是正确的[Rķ+1个Ë3。另一方面,使用加法数论的工具,我们提出了几种结构,这些证明表明猜想的下界部分是正确的。[R3ķ=2Ë=4578。在得出结果之前,所有与推测的下界匹配的已知构造都满足[R=3 要么 Ë=3。我们的构造是文献中第一个突破这一障碍的构造。

更新日期:2020-11-06
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