Disjunctive domination in graphs with minimum degree at least two

TL;DR

This paper investigates the disjunctive domination number in graphs with minimum degree at least two, establishing an upper bound for certain classes of graphs and exploring claw-free graphs.

Contribution

It proves an upper bound of |G|/3 for the disjunctive domination number in graphs with minimum degree at least two, excluding specific forbidden components, and examines claw-free graphs.

Findings

Bound of γ₂^d(G) ≤ |G|/3 for specified graphs

Identification of an infinite family of graphs attaining the bound

Analysis of disjunctive domination in claw-free graphs

Abstract

A set $D$ of vertices in $G$ is a disjunctive dominating set in $G$ if every vertex not in $D$ is adjacent to a vertex of $D$ or has at least two vertices in $D$ at distance $2$ from it in $G$. The disjunctive domination number, $\gamma^{d}_2(G)$, of $G$ is the minimum cardinality of a disjunctive dominating set in $G$. In this paper, we show that if $G$ be a graph of order at least $3$, $\delta(G)\geq 2$ and with no component isomorphic to any of eight forbidden graphs, then $\gamma^{d}_2(G)\leq \frac{|G|}{3}$. Moreover, we provide an infinite family of graphs attaining this bound. In addition, we also study the case that $G$ is a claw-free graph with minimum degree at least two.