Non-abelian Extensions of Lie algebras with derivations
In this paper, we investigate non-abelian extensions of Lie algebras with derivations from several different perspectives. We show that the theory of non-abelian extensions of a Lie algebra with a derivation can be characterized by means of the second non-abelian cohomology, the Deligne groupoid, the homotopy category of strict Lie $2$-algebras with strict derivations, and the notion of a $(\mathfrak{g}, D)$-kernel, respectively. Moreover, within this unified framework, we address the following existence problem: given a non-abelian extension of Lie algebras $$ 0\longrightarrow\mathfrak{h}\overset{i}\longrightarrow\hat{\mathfrak{g}}\overset{p}\longrightarrow\mathfrak{g}\longrightarrow 0, $$ let $(K,D)\in\mathrm{Der}(\mathfrak{h})\times\mathrm{Der}(\mathfrak{g})$ be a pair of derivations of $\mathfrak{h}$ and $\mathfrak{g}$ respectively. When does there exist a derivation $\hat{D}$ of $\hat{\mathfrak{g}}$ such that $\hat{D}|_{\mathfrak{h}}=K$ and $D\circ p=p\circ\hat{D}.$ We provide an obstruction class for the existence of such a lift.