Noetherian rings with almost injective simple modules

ABSTRACT

We characterize right Noetherian rings over which all simple modules are almost injective. It is proved that R is such a ring, if and only if, the complements of semisimple submodules of every R-module M are direct summands of M, if and only if, R is a finite direct sum of right ideals I_r, where I_r is either a Noetherian V-module with zero socle, or a simple module, or an injective module of length 2. A commutative Noetherian ring for which all simple modules are almost injective is precisely a finite direct product of rings R_i, where R_i is either a field or a quasi-Frobenius ring of length 2. We show that for commutative rings whose all simple modules are almost injective, the properties of Kasch, (semi)perfect, semilocal, quasi-Frobenius, Artinian, and Noetherian coincide.

KEYWORDS:

• Almost injective modules; almost V-rings; artinian serial rings

2010 MATHEMATICS SUBJECT CLASSIFICATION:

• 16D60
• 16D70
• 16P40

Acknowledgment

The authors wish to express their gratitude to the referee for a careful checking of the details and for helpful comments which improved this paper.