A Fan-type condition for cycles in $1$-tough and $k$-connected $(P_2\cup kP_1)$-free graphs

TL;DR

This paper establishes a new Fan-type condition involving the parameter _{k+1}(G) for cycles in 1-tough, k-connected, (P_2 _1)-free graphs, extending previous Hamiltonicity results.

Contribution

It generalizes existing Hamiltonian conditions for certain graph classes by introducing a novel parameter _{k+1}(G) and a corresponding theorem.

Findings

Graphs with _{k+1}(G)  _{7k-6/5} are Hamiltonian or Petersen.

The result applies to 1-tough, k-connected, (P_2 _1)-free graphs.

Extends previous connectivity and toughness conditions for Hamiltonicity.

Abstract

For a graph $G$, let $\mu_k(G):=\min~\{\max_{x\in S}d_G(x):~S\in \mathcal{S}_k\}$, where $\mathcal{S}_k$ is the set consisting of all independent sets $\{u_1,\ldots,u_k\}$ of $G$ such that some vertex, say $u_i$ ($1\leq i\leq k$), is at distance two from every other vertex in it. A graph $G$ is $1$-tough if for each cut set $S\subseteq V(G)$, $G-S$ has at most $|S|$ components. Recently, Shi and Shan \cite{Shi} conjectured that for each integer $k\geq 4$, being $2k$-connected is sufficient for $1$-tough $(P_2\cup kP_1)$-free graphs to be hamiltonian, which was confirmed by Xu et al. \cite{Xu} and Ota and Sanka \cite{Ota2}, respectively. In this article, we generalize the above results through the following Fan-type theorem: Let $k$ be an integer with $k\geq 2$ and let $G$ be a $1$-tough and $k$-connected $(P_2\cup kP_1)$-free graph with $\mu_{k+1}(G)\geq\frac{7k-6}{5}$, then $G$ is hamiltonian or the Petersen graph.