English

A note on two Conjectures on Dimension funcitons of $C^{*}$-algebras

Operator Algebras 2016-01-15 v1 Functional Analysis

Abstract

\noindent Let AA be an arbitrary CC^* algebra. In \cite{BH} Blackadar and Handelman conjectured the set of lower semicontinuous dimension functions on AA to be pointwise dense in the set DF(A)DF(A) of all dimension functions on AA and DF(A)DF(A) to be a Choquet simplex. We provide an equivalent condition for the first conjecture for unital AA. Then by applying this condition we confirm the first Conjecture for all unital AA for which either the radius of comparison is finite or the semigroup W(A)W(A) is almost unperforated. As far as we know the most general results on the first Conjecture up to now assumes exactness, simplicity and moreover stronger regularity properties such as strict comparison. Our results are achieved through applications of the techniques developed in \cite{BR} and \cite{R}. We also note that, whenever the first Conjecture holds for some unital AA and extreme boundary of the the quasitrace simplex of AA is finite, then every dimension function of AA is lower semicontinuous and DF(A)DF(A) is affinely homeomorphic to the quasitrace simplex of AA. Combing this with the said results on the first Conjecture give us a class of algebras for which DF(A)DF(A) is a Choquet simplex, i.e. gives a new class for which the 2nd Conjecture mentioned above holds.

Keywords

Cite

@article{arxiv.1601.03475,
  title  = {A note on two Conjectures on Dimension funcitons of $C^{*}$-algebras},
  author = {Kaushika De Silva},
  journal= {arXiv preprint arXiv:1601.03475},
  year   = {2016}
}
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