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Root Extensions and Factorization in Affine Domains

Published online by Cambridge University Press:  20 November 2018

P. Etingof
Affiliation:
Department of Mathematics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA e-mail: etingof@math.mit.edu
P. Malcolmson
Affiliation:
Department of Mathematics, Wayne State University, Detroit, MI 48202, USA e-mail: petem@math.wayne.edu e-mail: okoh@math.wayne.edu
F. Okoh
Affiliation:
Department of Mathematics, Wayne State University, Detroit, MI 48202, USA e-mail: petem@math.wayne.edu e-mail: okoh@math.wayne.edu
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Abstract

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An integral domain $R$ is IDPF (Irreducible Divisors of Powers Finite) if, for every non-zero element $a$ in $R$ , the ascending chain of non-associate irreducible divisors in $R$ of ${{a}^{n}}$ stabilizes on a finite set as $n$ ranges over the positive integers, while $R$ is atomic if every non-zero element that is not a unit is a product of a finite number of irreducible elements (atoms). A ring extension $S$ of $R$ is a root extension or radical extension if for each $s$ in $S$ , there exists a natural number $n\left( s \right)$ with ${{s}^{n\left( s \right)}}$ in $R$ . In this paper it is shown that the ascent and descent of the IDPF property and atomicity for the pair of integral domains $\left( R,\,S \right)$ is governed by the relative sizes of the unit groups $\text{U}\left( R \right)$ and $\text{U}\left( S \right)$ and whether $S$ is a root extension of $R$ . The following results are deduced from these considerations: An atomic IDPF domain containing a field of characteristic zero is completely integrally closed. An affine domain over a field of characteristic zero is IDPF if and only if it is completely integrally closed. Let $R$ be a Noetherian domain with integral closure $S$ . Suppose the conductor of $S$ into $R$ is non-zero. Then $R$ is IDPF if and only if $S$ is a root extension of $R$ and $\text{U}\left( S \right)/\text{U}\left( R \right)$ is finite.

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Type
Research Article
Copyright
Copyright © Canadian Mathematical Society 2010