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Linear cycles of consecutive lengths
Journal of Combinatorial Theory Series B ( IF 1.2 ) Pub Date : 2023-07-04 , DOI: 10.1016/j.jctb.2023.06.002
Tao Jiang , Jie Ma , Liana Yepremyan

A well-known result of Verstraëte [23] shows that for each integer k2 every graph G with average degree at least 8k contains cycles of k consecutive even lengths, the shortest of which is of length at most twice the radius of G. We establish two extensions of Verstraëte's result for linear cycles in linear r-uniform hypergraphs.

We show that for any fixed integers r3 and k2, there exist constants c1=c1(r) and c2=c2(r), such that every n-vertex linear r-uniform hypergraph G with average degree d(G)c1k contains linear cycles of k consecutive even lengths, the shortest of which is of length at most 2lognlog(d(G)/k)c2. In particular, as an immediate corollary, we retrieve the current best known upper bound on the linear Turán number of C2kr with improved coefficients.

Furthermore, we show that for any fixed integers r3 and k2, there exist constants c3=c3(r) and c4=c4(r) such that every n-vertex linear r-uniform hypergraph with average degree d(G)c3k, contains linear cycles of k consecutive lengths, the shortest of which has length at most 6lognlog(d(G)/k)c4+6. In both cases for given average degree d, the length of the shortest cycles cannot be improved up to the constant factors c2,c4.



中文翻译:

连续长度的线性循环

Verstraëte [23]的一个众所周知的结果表明,对于每个整数k2每个平均度数至少为 8 k的图G都包含k 个连续偶数长度的循环,其中最短的循环的长度最多为G半径的两倍。我们建立了 Verstraëte 在线性r均匀超图中的线性循环结果的两个扩展

我们证明对于任何固定整数r3k2, 存在常数C1=C1rC2=C2r,使得每个n顶点线性r均匀超图G具有平均度dGC1k包含k 个连续偶数长度的线性循环,其中最短的长度最多为2日志n日志dG/k-C2。特别是,作为直接推论,我们检索了当前最著名的线性图兰数上限C2kr具有改进的系数。

此外,我们证明对于任何固定整数r3k2, 存在常数C3=C3rC4=C4r使得每个n顶点线性r均匀超图具有平均度dGC3k,包含k 个连续长度的线性循环,其中最短的长度最多6日志n日志dG/k-C4+6。在这两种情况下,对于给定的平均度d,最短周期的长度不能提高到常数因子C2,C4

更新日期:2023-07-05
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