English

Weakly-morphic modules

Rings and Algebras 2022-05-30 v1 Commutative Algebra Representation Theory

Abstract

Let RR be a commutative ring, MM an RR-module and φa\varphi_a be the endomorphism of MM given by right multiplication by aRa\in R. We say that MM is {\it weakly-morphic} if M/φa(M)ker(φa)M/\varphi_a(M)\cong \ker(\varphi_a) as RR-modules for every aa. We study these modules and use them to characterise the rings R/AnnR(M)R/\text{Ann}_R(M), where AnnR(M)\text{Ann}_R(M) is the right annihilator of MM. A kernel-direct or image-direct module MM is weakly-morphic if and only if each element of R/AnnR(M)R/\text{Ann}_R(M) is regular as an endomorphism element of MM. If MM is a weakly-morphic module over an integral domain RR, then MM is torsion-free if and only if it is divisible if and only if R/AnnR(M)R/\text{Ann}_R(M) is a field. A finitely generated Z\Bbb Z-module is weakly-morphic if and only if it is finite; and it is morphic if and only if it is weakly-morphic and each of its primary components is of the form (Zpk)n(\Bbb Z_{p^k})^n for some non-negative integers nn and kk.

Keywords

Cite

@article{arxiv.2205.13794,
  title  = {Weakly-morphic modules},
  author = {Philly Ivan Kimuli and David Ssevviiri},
  journal= {arXiv preprint arXiv:2205.13794},
  year   = {2022}
}

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20 pages