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Extreme points of unital completely positive maps invariant under partial action

Operator Algebras 2025-07-29 v1

Abstract

The classical Choquet theorem establishes a barycentric decomposition for elements in a compact convex subset of a locally convex topological vector space. This decomposition is achieved through a probability measure that is supported on the set of extreme points of the subset. In this work, we consider a partial action τ\tau of a group GG on a CC^\ast-algebra A\mathcal{A}. For a fixed Hilbert space H\mathcal{H}, we consider the set of all unital completely positive maps from A\mathcal{A} to B(H)\mathcal{B}(\mathcal{H}) that are invariant under the partial action τ\tau. This set forms a compact convex subset of a locally convex topological vector space. To complete the picture of the barycentric decomposition provided by the classical Choquet theorem, we characterize the set of extreme points of this set.

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Cite

@article{arxiv.2507.20797,
  title  = {Extreme points of unital completely positive maps invariant under partial action},
  author = {Chaitanya J. Kulkarni and Md Amir Hossain},
  journal= {arXiv preprint arXiv:2507.20797},
  year   = {2025}
}

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16 pages