Lifts of endomorphisms of Weyl algebras modulo $p^2$

Abstract

Let $\phi$ denote a $k$-algebra endomorphism of the $n$-th Weyl algebra $A_n(k)$ over a perfect field $k$ of positive characteristic $p$. We prove that $\phi$ can be lifted to an endomorphism of the Weyl algebra $A_n(W_2(k))$ over the Witt vectors $W_2(k)$ of length two over $k$ if and only if $\phi$ induces a Poisson morphism of the center of $A_n(k)$. Furthermore, we improve a result of Tsuchimoto, which enables us to conclude that these equivalent statements hold at least when $\mathrm{deg}(\phi )<p$. In particular, we conclude that $\phi$ is injective if $\mathrm{deg}(\phi )<p$.