Complexity rank for C∗-algebras
Complexity rank for C∗-algebras
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发表时间:
2022
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通讯作者:
A. Jaime;R. Willett
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作者:
A. Jaime;R. Willett
Complexity rank for C∗-algebras was introduced by the second author and Yu for applications towards the UCT: very roughly, this rank is at most n if you can repeatedly cut the C∗-algebra in half at most n times, and end up with something finite dimensional. In this paper, we study complexity rank, and also a weak complexity rank that we introduce; having weak complexity rank at most one can be thought of as ‘two-colored local finite-dimensionality’. We first show that for separable, unital, and simple C∗-algebras, weak complexity rank one is equivalent to the conjunction of nuclear dimension one and real rank zero. In particular, this shows that the UCT for all nuclear C∗-algebras is equivalent to equality of the weak complexity rank and the complexity ranks for Kirchberg algebras with zero K-theory groups. However, we also show using a K-theoretic obstruction (torsion in K1) that weak complexity rank one and complexity rank one are not the same in general. We then use the Kirchberg-Phillips classification theorem to compute the complexity rank of all UCT Kirchberg algebras: it is always one or two, with the rank one case occurring if and only if the K1-group is torsion free. University of Hawai‘i at Mānoa, 2565 McCarthy Mall, Keller 401A, Honolulu, HI 96816, USA; ajaime@hawaii.edu. University of Hawai‘i at Mānoa, 2565 McCarthy Mall, Keller 401A, Honolulu, HI 96816, USA; rufus@math.hawaii.edu. 1 ar X iv :2 20 5. 04 70 4v 2 [ m at h. O A ] 1 1 O ct 2 02 2