$\sqrtΔ$-Fine Rings

Abstract

We introduce and study the so-termed {\it $\sqrtΔ$-fine rings}, a new class of rings that generalizes the classical {\it fine rings} introduced by Călugăreanu-Lam in J. Algebra \& Appl. (2016) by requiring that every nonzero element $r \in R$ can be written as $r = u + a$, where $u$ is a unit and $a \in \sqrt{Δ(R)}$. We establish that every such ring is simple, every abelian $\sqrtΔ$-fine ring is indecomposable, and most notably, the matrix ring $M_n(R)$ over a $\sqrtΔ$-fine ring $R$ is again $\sqrtΔ$-fine for every $n \ge 1$. As a consequence, we characterize all semi-local $\sqrtΔ$-fine rings as those rings which are precisely the simple Artinian rings. We also examine group rings, providing conditions under which they are either $\sqrtΔ$-fine or generalized fine, where the latter class was introduced by Zhou in J. Algebra \& Appl. (2022), and conclude our work with the difficult open question asking of whether each $\sqrtΔ$-fine ring is necessarily fine.