Core and Dual Core Inverses of a Sum of Morphisms

TL;DR

This paper characterizes the existence and explicit form of core and dual core inverses of sums of morphisms in additive categories with involution, and extends results to elements in rings with Jacobson radical.

Contribution

It provides necessary and sufficient conditions for the core inverse of a sum of morphisms and rings elements, including explicit formulas, extending prior work in generalized inverse theory.

Findings

Core inverse of sum characterized by invertibility conditions.

Explicit formula for the core inverse of the sum provided.

Extension of results to ring elements with Jacobson radical.

Abstract

Let $\mathscr{C}$ be an additive category with an involution $\ast$. Suppose that $\varphi : X \rightarrow X$ is a morphism of $\mathscr{C}$ with core inverse $\varphi^{\co} : X \rightarrow X$ and $\eta : X \rightarrow X$ is a morphism of $\mathscr{C}$ such that $1_X+\varphi^{\co}\eta$ is invertible. Let $\alpha=(1_X+\varphi^{\co}\eta)^{-1},$ $\beta=(1_X+\eta\varphi^{\co})^{-1},$ $\varepsilon=(1_X-\varphi\varphi^{\co})\eta\alpha(1_X-\varphi^{\co}\varphi),$ $\gamma=\alpha(1_X-\varphi^{\co}\varphi)\beta^{-1}\varphi\varphi^{\co}\beta,$ $\sigma=\alpha\varphi^{\co}\varphi\alpha^{-1}(1_X-\varphi\varphi^{\co})\beta,$ $\delta=\beta^{\ast}(\varphi^{\co})^{\ast}\eta^{\ast}(1_X-\varphi\varphi^{\co})\beta.$ Then $f=\varphi+\eta-\varepsilon$ has a core inverse if and only if $1_X-\gamma$, $1_X-\sigma$ and $1_X-\delta$ are invertible. Moreover, the expression of the core inverse of $f$ is presented. Let $R$ be a unital $\ast$-ring and $J(R)$ its Jacobson radical, if $a\in R^{\co}$ with core inverse $a^{\co}$ and $j\in J(R)$, then $a+j\in R^{\co}$ if and only if $(1-aa^{\co})j(1+a^{\co}j)^{-1}(1-a^{\co}a)=0$. We also give the similar results for the dual core inverse.