Isomorphism problems and groups of automorphisms for Ore extensions $K[x][y; \delta ]$ (zero characteristic)

Abstract

Let $\L (f) = K[x][y; f\frac{d}{dx} ]$ be an Ore extension of a polynomial algebra $K[x]$ over a field $K$ of characteristic zero where $f\in K[x]$. For a given polynomial $f$, the automorphism group of the algebra $\L (f) $ is explicitly described. The polynomial case $\L (0) = K[x,y]$ and the case of the Weyl algebra $A_1= K[x][y; \frac{d}{dx} ]$ were done done by Jung (1942) and van der Kulk (1953), and Dixmier (1968), respectively. In 1997, Alev and Dumas proved that the algebras $\L (f)$ and $\L (g)$ are isomorphic iff $g(x) = \l f(\alpha x+\beta )$ for some $\l, \alpha \in K\backslash \{ 0\}$ and $\beta\in K$. In 2015, Benkart, Lopes and Ondrus gave a complete description of the set of automorphism groups of algebras $\L(f)$. In this paper we complete the picture, i.e. {\em given} the polynomial $f$ we have the explicit description of the automorphism group of $\L (f)$.