English

Sufficient conditions for $(K_2 \cup kK_1)$-free graphs to be Hamilton-connected

Combinatorics 2026-07-13 v1

Abstract

The toughness of a non-complete graph GG, denoted τ(G)\tau(G), is defined as τ(G)=min{Sω(GS):SV(G), ω(GS)2}, \tau(G) = \min\left\{ \frac{|S|}{\omega(G-S)} : S \subseteq V(G),\ \omega(G-S) \geq 2 \right\}, where ω(GS)\omega(G-S) is the number of components of GSG - S. For a complete graph GG, we define τ(G)=\tau(G) = \infty. A graph GG is tt-tough if τ(G)t\tau(G) \geq t. For a positive integer kk, a graph GG is (K2kK1)(K_2 \cup kK_1)-free if it contains no induced subgraph isomorphic to K2kK1K_2 \cup kK_1. Recently, Liu \cite{liu} showed that every 2k2k-connected (K2kK1)(K_2 \cup kK_1)-free graph GG with τ(G)>1\tau(G) > 1 is Hamilton-connected. In this paper, we strengthen this result by proving that every (k+1)(k+1)-connected (K2kK1)(K_2 \cup kK_1)-free graph GG with τ(G)>1\tau(G) > 1 and minimum degree δ(G)2k\delta(G) \geq 2k is Hamilton-connected. Moreover, by imposing restrictions to the independence number α(G)\alpha(G), we prove that every kk-connected (K2kK1)(K_2 \cup kK_1)-free graph GG of order nn with 2k+1α(G)<n22k+1 \leq \alpha(G) < \frac{n}{2} and δ(G)2k\delta(G) \geq 2k is Hamilton-connected, and that the bounds on α(G)\alpha(G) are sharp.

Keywords

Cite

@article{arxiv.2607.11373,
  title  = {Sufficient conditions for $(K_2 \cup kK_1)$-free graphs to be Hamilton-connected},
  author = {Xiaoqiong Xu and Shujie Chen and Fengming Dong and Tao Tian},
  journal= {arXiv preprint arXiv:2607.11373},
  year   = {2026}
}