Eternal domination in Cayley graphs

Abstract

Eternal domination is a process in which a set of guards occupying a dominating set on a graph protects against an infinite sequence of attacks. After a vertex is attacked, one guard must move along an edge to the attacked vertex and each of the remaining guards may move along an edge so that the guards again occupy a dominating set on the graph and can defend the next attack. The minimum number of guards needed in a graph $Γ$ is the eternal domination number, denoted by $γ_{\mathrm{all}}^\infty(Γ)$. In this paper, we show that the eternal domination number of a vertex-transitive graph with an efficient dominating set is equal to its domination number. We show that a Cayley graph on a generalized dihedral group whose connection set contains few or many reflections is efficiently dominated. Then, we provide an infinite family of connected Cayley graphs for which $γ_{\mathrm{all}}^{\infty}(Γ) = γ(Γ)+1$, generalizing a result of [Braga et al., J. Combin. Math. Combin. Comput. 96 (2016), 13--22]. Finally, we build an infinite family of connected Cayley graphs with $γ_{\mathrm{all}}^\infty(Γ) \geq γ(Γ)+2$.