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https://dx.doi.org/10.48550/ar...
Article . 2011
License: arXiv Non-Exclusive Distribution
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Strong connectivity and directed triangles in oriented graphs. Partial results on a particular case of the Caccetta-H��ggkvist conjecture

Authors: Lichiardopol, Nicolas;

Strong connectivity and directed triangles in oriented graphs. Partial results on a particular case of the Caccetta-H��ggkvist conjecture

Abstract

A particular case of Caccetta-H��ggkvist conjecture, says that a digraph of order $n$ with minimum out-degree at least $1/3n$ contains a directed cycle of length at most 3. Recently, Kral, Hladky and Norine proved that a digraph of order $n$ with minimum out-degree at least $0.3465n$ contains a directed cycle of length at most 3 (which currently is the best result). A weaker particular case says that a digraph of order $n$ with minimum semi-degree at least $1/3n$ contains a directed triangle. In a recent paper, by using the result of Kral et al, the author proved that for $��\geq 0.343545$, any digraph $D$ of order $n$ with minimum semi-degree at least $��n$ contains a directed cycle of length at most 3 (which currently is the best result). This means that for a given integer $d\geq 1$, every digraph with minimum semi-degree $d$ and of order $md$ with $m\leq 2.91082$, contains a directed cycle of length at most 3. In particular, every oriented graph with minimum semi-degree $d$ and of order $md$ with $m\leq 2.91082$, contains a directed triangle. In this paper, by using the result of Kral et al, we prove that every oriented graph with minimum semi-degree $d$, of order $md$ with $2.91082< m\leq 3$ and of strong connectivity at most $0.679d$, contains a directed triangle. This will be implied by a more general and more precise result, valid not only for $2.91082< m\leq 3$ but also for larger values of $m$. As application, we improve two existing results. The first result (Authors Broersma and Li), concerns the number of the directed cycles of length 4 of a triangle free oriented graph of order $n$ and of minimum semi-degree at least $\frac{n}{3}$. The second result (Authors Kelly, K��hn and Osthus), concerns the diameter of a triangle free oriented graph of order $n$ and of minimum semi-degree at least $\frac{n}{5}$.

14 pages

Keywords

FOS: Mathematics, Mathematics - Combinatorics, Combinatorics (math.CO)

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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
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