The existence of planar $4$-connected essentially $6$-edge-connected graphs with no claw-decompositions

TL;DR

This paper constructs smaller counterexamples to a conjecture on claw-decompositions in planar graphs, showing that certain highly connected graphs can lack such decompositions, thus highlighting the sharpness of known conditions.

Contribution

It provides a smaller counterexample with 18 vertices and introduces a family of planar 4-connected essentially 6-edge-connected graphs without claw-decompositions.

Findings

Counterexamples with 18 vertices disprove previous conjectures.

Constructs a family of graphs with no claw-decompositions.

Shows sharpness of conditions for claw-decompositions in highly connected graphs.

Abstract

In 2006 Bar{\'a}t and Thomassen conjectured that every planar $4$-edge-connected $4$-regular simple graph of size divisible by three admits a claw-decomposition. Later, Lai (2007) disproved this conjecture by a family of planar graphs with edge-connectivity $4$ which the smallest one contains $24$ vertices. In this note, we first give a smaller counterexample having only $18$ vertices and next construct a family of planar $4$-connected essentially $6$-edge-connected $4$-regular simple graphs of size divisible by three with no claw-decompositions. This result provides the sharpness for two known results which say that every $5$-edge-connected graph of size divisible by three admits a claw-decomposition if it is essentially $6$-edge-connected or planar.