Topologically semisimple and topologically perfect topological rings

TL;DR

This paper extends classical semisimple and perfect ring theories to topological rings, establishing conditions for semisimplicity and perfect decompositions, and exploring their implications in topologically agreeable categories.

Contribution

It introduces new topological analogues of semisimple and perfect rings, proving their equivalences and connections to module decompositions and additive categories.

Findings

Semisimplicity of contramodules is equivalent to that of discrete modules.

Conditions for topologically perfect rings are shown to be equivalent under certain topological constraints.

Modules with perfect decomposition are characterized in terms of endomorphism rings and topologically agreeable categories.

Abstract

Extending the Wedderburn-Artin theory of (classically) semisimple associative rings to the realm of topological rings with right linear topology, we show that the abelian category of left contramodules over such a ring is split (equivalently, semisimple) if and only if the abelian category of discrete right modules over the same ring is split (equivalently, semisimple). Our results in this direction complement those of Iovanov-Mesyan-Reyes. An extension of the Bass theory of left perfect rings to the topological realm is formulated as a list of conjecturally equivalent conditions, many equivalences and implications between which we prove. In particular, all the conditions are equivalent for topological rings with a countable base of neighborhoods of zero and for topologically right coherent topological rings. Considering the rings of endomorphisms of modules as topological rings with the finite topology, we establish a close connection between the concept of a topologically perfect topological ring and the theory of modules with perfect decomposition. Our results also apply to endomorphism rings and direct sum decompositions of objects in certain additive categories more general than the categories of modules; we call them topologically agreeable categories. We show that any topologically agreeable split abelian category is Grothendieck and semisimple. We also prove that a module $\Sigma$-coperfect over its endomorphism ring has a perfect decomposition provided that either the endomorphism ring is commutative or the module is countably generated, partially answering a question of Angeleri Hugel and Saorin.