Straight Rings

Abstract

A (commutative integral) domain is called a straight domain if A ↪ B is a prime morphism for each overring B of A; a (commutative unital) ring A is called a straight ring if A/P is a straight domain for all P ∈ Spec(A). A domain is a straight ring if and only if it is a straight domain. The class of straight rings sits properly between the class of locally divided rings and the class of going-down rings. An example is given of a two-dimensional going-down domain that is not a straight domain. The classes of straight rings, of locally divided rings, and of going-down rings coincide within the universe of seminormal weak Baer rings (for instance, seminormal domains). The class of straight rings is stable under formation of homomorphic images, rings of fractions, and direct limits. The “straight domain" property passes between domains having the same prime spectrum. Straight domains are characterized within the universe of conducive domains. If A is a domain with a nonzero ideal I and quotient field K, characterizations are given for A ↪ (I: _K I) to be a prime morphism. If A is a domain and P ∈ Spec(A) such that A _P is a valuation domain, then the CPI-extension C(P) := A + PA _P is a straight domain if and only if A/P is a straight domain. If A is a going-down domain and P ∈ Spec(A), characterizations are given for A ↪ C(P) to be a prime morphism. Consequences include divided domain-like behavior of arbitrary straight domains.

Key Words:

• CPI-extension
• Divisorial domain
• Flat
• Going-down
• Going-down domain
• Locally divided ring
• Prime morphism
• Prüfer domain
• Pseudo-valuation domain
• QQR-domain
• Seminormal
• Torsion-free
• Unibranched

2000 Mathematics Subject Classification:

• Primary 13G05, 13B24, 13B99, 13C99
• Secondary 13F45, 13A15, 13F05, 13E10

ACKNOWLEDGMENT

Dobbs was supported in part by a University of Tennessee Professional Leave Award.

Notes

Communicated by J. Kuzmanovich.