Title
Arc-disjoint in- and out-branchings in digraphs of independence number at most 2
Abstract
We prove that every digraph of independence number at most 2 and arc-connectivity at least 2 has an out-branching B + and an in-branching B - which are arc-disjoint (we call such branchings a good pair). This is best possible in terms of the arc-connectivity as there are infinitely many strong digraphs with independence number 2 and arbitrarily high minimum in- and out-degrees that have no good pair. The result settles a conjecture by Thomassen for digraphs of independence number 2. We prove that every digraph on at most 6 vertices and arc-connectivity at least 2 has a good pair and give an example of a 2-arc-strong digraph D on 10 vertices with independence number 4 that has no good pair. We also show that there are infinitely many digraphs with independence number 7 and arc-connectivity 2 that have no good pair. Finally we pose a number of open problems.
Year
DOI
Venue
2022
10.1002/jgt.22779
JOURNAL OF GRAPH THEORY
Keywords
DocType
Volume
arc-connectivity, arc-disjoint branchings, digraphs of independence number 2, in-branching, out-branching
Journal
100
Issue
ISSN
Citations 
2
0364-9024
0
PageRank 
References 
Authors
0.34
0
4
Name
Order
Citations
PageRank
Bang-Jensen Joergen100.34
Stéphane Bessy211719.68
Frédéric Havet343355.15
Anders Yeo41225108.09