Classifications of prime ideals and simple modules of the quantum Weyl algebra $A_1(q)$ ($q$ is a root of unity)

Abstract

This paper consists of three parts: (I) To develop general theory of a (large) class of central simple finite dimensional algebras and answering some natural questions about them (that in general situation it is not even clear how to approach them, and the Brauer group is a step in the right directions), (II) To introduce and develop general theory of a large class of rings, PLM-rings, (intuitively, they are the most general form of Quillen' Lemma), and (III) to apply these results for the following four classic algebras that turned out to be PLM-rings. Let $K$ be an arbitrary field and $q\in K\backslash \{ 0,1\}$ be a primitive $n$'th root of unity. Classifications of prime, completely prime, maximal and primitive ideals, and simple modules are obtained for the quantum Weyl algebra $A_1(q)=K\langle x,y \, | \, xy-qyx =1\rangle$, the skew polynomial algebra $\mathbb{A} = K[h][x;σ]$, the skew Laurent polynomial algebras $\mathcal{A} := K[h][x^{\pm 1};σ]$, and $\mathcal{B} := K[h^{\pm 1}][x^{\pm 1};σ]$ where $σ(h) = qh$. The quotient rings (of fractions) of prime factor algebras of the algebras $A_1$, $\mathbb{A}$, $\mathcal{A}$, and $\mathcal{B}$ are explicitly described. Each quotient ring is a central simple finite dimensional algebra, i.e., isomorphic to the matrix algebra $M_d(D)$ for some $d\geq 1$ and a central simple division algebra $D$. The division algebra $D$ is either a finite field extension of $K$ or a {\em cyclic} algebra. These descriptions are a key fact in the classifications of prime ideals, completely prime ideals, and simple modules for the algebras above. For each simple module its basis, dimension, and endomorphism algebra are given. Explicit descriptions are obtained for the automorphism groups of the algebras $A_1$, $\mathbb{A}$, $\mathcal{A}$, and $\mathcal{B}$.