Strong subgraph 2-arc-connectivity of Cartesian product of digraphs

Let $D=(V,A)$ be a digraph of order $n$, $S$ a subset of $V$ of size $k$ and $2\le k\leq n$. A strong subgraph $H$ of $D$ is called an $S$-strong subgraph if $S\subseteq V(H)$. A pair of $S$-strong subgraphs $D_1$ and $D_2$ are said to be arc-disjoint if $A(D_1)\cap A(D_2)=\emptyset$. Let $\lambda_S(D)$ be the maximum number of arc-disjoint $S$-strong subgraphs in $D$. The strong subgraph $k$-arc-connectivity is defined as $$\lambda_k(D)=\min\{\lambda_S(D)\mid S\subseteq V(D), |S|=k\}.$$ The parameter $\lambda_k(D)$ could be seen as a generalization of classical edge-connectivity of undirected graphs. In this paper, we study the strong subgraph 2-arc-connectivity of Cartesian product $\lambda_2(G\Box H)$ of two digraphs $G$ and $H$. We prove that $\lambda_2(G\Box H)\ge \lambda_2(G)+\lambda_2(H)-1$ but there is no linear upper bound for $\lambda_2(G\Box H)$ in terms of $\lambda_2(G)$ and $\lambda_2(H).$ We also obtain exact values for $\lambda_2(G\Box H)$, where $G$ and $H$ are digraphs from some digraph families.