arXiv subjects

Craig Kleski

Publications and source records attributed to Craig Kleski.

3 recordsLinked to original sources

arXiv2015

Classification of C*-algebras generated by representations of the unitriangular group $UT(4,\mathbb{Z})$

It was recently shown that each C*-algebra generated by a faithful irreducible representation of a finitely generated, torsion free nilpotent group is classified by its ordered K-theory. For the three step nilpotent group $UT(4,\mathbb{Z})$ we calculate the ordered K-theory of each C*-algebra generated by a faithful irreducible representation of $UT(4,\mathbb{Z})$ and see that they are all simple A$\mathbb{T}$ algebras. We also point out that there are many simple non A$\mathbb{T}$ algebras generated by irreducible representations of nilpotent groups.

math.OA↗

arXiv2015

Korovkin-type properties for completely positive maps

We prove a noncommutative variant of Saskin's classical theorem -- on the connection between Choquet boundaries for function spaces and Korovkin sets -- for operator systems generating separable Type I C*-algebras. The main result implies an affirmative answer to a weaker version of Arveson's hyperrigidity conjecture for such C*-algebras. It also yields information about the more general version of Arveson's conjecture.

math.OA↗

arXiv2011

Boundary representations and pure completely positive maps

In 2006, Arveson resolved a long-standing problem by showing that for any element $x$ of a separable self-adjoint unital subspace $S\subseteq B(H)$, $\|x\|=\sup\|π(x)\|$, where $π$ runs over the boundary representations for $S$. Here we show that "sup" can be replaced by "max". This implies that the Choquet boundary for a separable operator system is a boundary in the classical sense; a similar result is obtained in terms of pure matrix states when $S$ is not assumed to be separable. For matrix convex sets associated to operator systems in matrix algebras, we apply the above results to improve the Webster-Winkler Krein-Milman theorem.

math.OA↗