Centralizers of Jacobian derivations

Abstract

Let $\mathbb K$ be an algebraically closed field of characteristic zero, $\mathbb K[x, y]$ the polynonial ring in variables $x$, $y$ and let $W_2(\mathbb K)$ be the Lie algebra of all $\mathbb K$-derivations on $\mathbb K[x, y]$. A derivation $D \in W_2(\mathbb K)$ is called a Jacobian derivation if there exists $f \in \mathbb K[x, y]$ such that $D(h) = \det J(f, h)$ for any $h \in \mathbb K[x, y]$ (here $J(f, h)$ is the Jacobian matrix for $f$ and $h$). Such a derivation is denoted by $D_f$. The kernel of $D_f$ in $\mathbb K[x, y]$ is a subalgebra $\mathbb K[p]$ where $p=p(x, y)$ is a polynomial of smallest degree such that $f(x, y) = \varphi (p(x, y)$ for some $\varphi (t) \in \mathbb K[t]$. Let $C = C_{W_2(\mathbb K)} (D_f)$ be the centralizer of $D_f$ in $W_2(\mathbb K)$. We prove that $C$ is the free $\mathbb K[p]$-module of rank 1 or 2 over $\mathbb K[p]$ and point out a criterion of being a module of rank $2$. These results are used to obtain a class of integrable autonomous systems of differential equations.