MathOverflow Asked on November 9, 2021
Let $mathcal{L}$ be a finite first-order language with no relation symbols, and $mathcal{K}:=mathcal{V}(Theta)$ a variety in this language definited by a set of identities $Theta$.
My questions are motivated, of course, by Noether’s Theorem in invariant theory, and Chevalley-Shephard-Todd theorem (which can be seem as statements in the variety of commutative associative algebras) for algebraic systems (using Malcev terminology).
Question 1
Let $A$ be a finitely generated algebraic system in $mathcal{K}$, and $G$ a finite group acting by $mathcal{K}$-automorphisms on $A$. When is $A^G:={a in A| g.a=a, forall g in G}$, again finitely generated? A subcase of important interest is when $A$ is a relatively free algebraic system of $mathcal{K}$.
Question 2
Let $A$ be a finitely generated and relatively free algebraic system in $mathcal{K}$ and $G$ be a finite group of automorphisms as above. When is $A^G$ is a (possibly infinitely generated) relatively free algebraic system of $mathcal{K}$ itself?
For varieties of associative algebras the work on Questions 1 and 2 has reached a very mature form (cf. Formanek, Noncommutative invariant theory, MR0810646). There has been an intensive study of these questions for varieties of Lie algebras by a number of people (V. Drenksy, V. Petrogradskii, etc) but I know of no work for other important variaties of non-associative algebras (such as Jordan algebras, alternative algebras, Malcev algebras, etc), and also nothing about general algebraic systems.
Refinement of Questions 1 and 2 Is there any general result in Universal algebra (or Model theory) that is relevant for the pourposes of these questions? Is something known about variaties of non-associative algebras (other than Lie)?
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