Generalized Weyl Algebras (GWAs) appear in diverse areas of mathematics including mathematical physics, noncommutative algebra, and representation theory. We study the invariants of quantum GWAs under finite automorphisms. We extend a theorem of Jordan and Wells and apply it to determine the fixed ring of quantum GWAs under diagonal automorphisms. We further study properties of the fixed rings, including global dimension, rigidity, and simplicity.
IntroductionThroughout, k is a field and all algebras are associative k-algebras.The Shephard-Todd-Chevalley (STC) Theorem [6,24] gives conditions for the fixed ring of a polynomial ring by a finite group of linear automorphisms to again be a polynomial ring. More recently, there has been significant interest in studying STC-like theorems in noncommutative algebra, in particular whether the fixed ring of an (N-graded) Artin-Schelter regular algebra again has this property [15].To consider this problem outside of the N-graded setting, one could ask whether the fixed ring of a (twisted) Calabi-Yau algebra is again (twisted) Calabi-Yau. Algebras satisfying this property have attracted much interest of late [9,18,20,21]. Since polynomial rings are (trivially) Calabi-Yau, this is indeed a reasonable generalization.An important family of Z-graded (twisted) Calabi-Yau algebras are the generalized Weyl algebras (GWAs) and so they serve as a good test case of the STC question in this setting. Kirkman and Kuzmanovich [16] have proposed a version of the STC Theorem for GWAs, essentially asking when the fixed ring of a GWA again has GWA structure. We propose a strengthening of this: to determine when the fixed ring of a Calabi-Yau GWA is again a Calabi-Yau GWA.Generalized Weyl algebras were named by Bavula [2]. They have been studied extensively by many authors prior to and post Bavula's definition. Notably, the interested reader is directed to the work of Hodges [10, 11], Jordan [12], Joseph [14], Rosenberg [23], Smith [26], and Stafford [27]. There are severalimportant families of algebras that may be constructed as GWAs. In the classical case, this includes the Weyl algebras and primitive quotients of U (sl 2 ). We will primarily be concerned with a subclass known as quantum GWAs, which includes quantum planes, quantum Weyl algebras, and primitive quotients of U q (sl 2 ).The proposal of Kirkman and Kuzmanovich [16] mentioned above has its basis in the work of Jordan and Wells [13] and their study of fixed rings of GWAs by automorphisms that fix the base ring. Won and the first-named author showed that it is possible to diagonalize any filtered automorphism of a classical GWA 1 with quadratic defining polynomial so that the Jordan and Wells result may be applied [8]. The methods and results in this paper vary wildly from these aforementioned works.Results. First, in Section 2, we study automorphisms of quantum GWAs. We use the classification of their automorphism groups by Suárez-Alvarez and Vivas [28] in order to classify their finite subgroups (Proposition 2.6). In Section 3 w...