Lie algebra generated by locally nilpotent derivations on Danielewski surfaces

Abstract

We give a full description of the Lie algebra generated by locally nilpotent derivations (short LNDs) on smooth Danielewski surfaces $D_p$ given by $xy=p(z)$. In case $\mathrm{deg}(p)\geq 3$ it turns out to be not the whole Lie algebra $\mathrm{VF}_{alg}^ω(D_p)$ of volume preserving algebraic vector fields, thus answering a question posed by Lind and the first author. Also we show algebraic volume density property (short AVDP) for a certain homology plane, a homogeneous space of the form $SL_2 (\mathbb{C}) /N$, where $N$ is the normalizer of the maximal torus and another related example. At the end of the paper we show by example that for the group of holomorphic automorphisms of a Stein manifold (endowed with c.-o. topology) the connected component and the path-connected component of the identity may not coincide.