An asymptotic bound for the Bermond--Thomassen Conjecture

Abstract

The Bermond--Thomassen Conjecture asserts that every digraph with minimum out-degree at least $2k-1$ contains $k$ disjoint directed cycles; it remains open in general. We asymptotically resolve it: there exist an absolute constant $K$ and a function $g(k)=o(k)$, independent of $n$, such that every $n$-vertex finite simple loopless digraph with minimum out-degree at least $2k+g(k)$ contains $k$ disjoint directed cycles for all integers $k\ge K$ and $n\ge1$. In fact we obtain the explicit error term $g(k)=O(k^{3/4}\sqrt{\log k})$.