Strong perforation in infinitely generated K_0-groups of simple C*-algebras

Abstract

Let (G,G^+) be a simple ordered abelian group. We say that G has strong perforation if there exists a non-positive element x in G such that nx is positive and non-zero for some natural number n. Otherwise, the group is said to be weakly unperforated. Examples of simple C*-algebras whose ordered K_0-groups have this property and for which the entire order structure on K_0 is known have, until now, been restricted to the case where K_0 is group isomorphic to the integers. We construct simple, separable, unital C*-algebras with strongly perforated K_0-groups group isomorphic to an arbitrary infinitely generated subgroup of the rationals, and determine the order structure on K_0 in each case.