Packing arborescences in random digraphs

Abstract

We study the problem of packing arborescences in the random digraph $\mathcal D(n,p)$, where each possible arc is included uniformly at random with probability $p=p(n)$. Let $\lambda(\mathcal D(n,p))$ denote the largest integer $\lambda\geq 0$ such that, for all $0\leq \ell\leq \lambda$, we have $\sum_{i=0}^{\ell-1} (\ell-i)|\{v: d^{in}(v) = i\}| \leq \ell$. We show that the maximum number of arc-disjoint arborescences in $\mathcal D(n,p)$ is $\lambda(\mathcal D(n,p))$ a.a.s. We also give tight estimates for $\lambda(\mathcal D(n,p))$ depending on the range of $p$.