Double total domination in the generalized lexicographic product of graphs

Abstract

Let G be a graph of minimum degree at least two. A set D ⊆ V(G) is said to be a double total dominating set of G if |N (v) ∩ D| ≥ 2 for every vertex v ∈ V(G). The double total domination number of G, denoted by γ_×2,t (G), is the minimum cardinality among all double total dominating sets of G. In this paper, we study this parameter for any generalized lexicographic product graph . In particular, we show that , where represents the total {2}-domination number of . Moreover, we obtain tight bounds and closed formulas on the double total domination number of this specific product of graphs in terms of domination invariants of the factor graphs. Finally, we characterize the graphs for which takes small values.