dorsal/arxiv
View SchemaUniqueness for embeddings of nuclear $C^*$-algebras into type II$_{1}$ factors
| Authors | Shanshan Hua, Stuart White |
|---|---|
| Categories | |
| ArXiv ID | 2601.08779vv1 |
| URL | https://arxiv.org/abs/2601.08779 |
| License | http://creativecommons.org/licenses/by/4.0/ |
Abstract
Let $A$ be a separable, unital and exact $C^*$-algebra satisfying the universal coefficient theorem. We prove uniqueness theorems up to unitary conjugacy for unital, full and nuclear maps from $A$ into ultraproducts of finite von Neumann factors: any two such maps agreeing on traces and total $K$-theory are unitarily equivalent. There are two consequences. Firstly if one takes the factors to be a sequence $(M_{k_n})_{n}$ of matrix algebras, we obtain a uniqueness result for quasidiagonal approximations of $A$. Secondly, when $(\mathcal M,\tau_{\calM})$ is a II$_1$ factor, a pair $\phi,\psi:A\to\mathcal M$ of unital, injective and nuclear maps are norm approximately unitarily equivalent if and only if $\tau_{\calM}\circ\phi=\tau_{\calM}\circ\psi$. The main strategy is to use Schafhauser's classification of lifts along the trace--kernel extension. Since our codomains may lack the tensorial absorption properties needed in this work, the main new ingredient is a suitable $KK$-uniqueness theorem tailored to our situation. This is inspired by $KK$-uniqueness theorems of Loreaux, Ng and Sutradhar.
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"abstract": "Let $A$ be a separable, unital and exact $C^*$-algebra satisfying the universal coefficient theorem. We prove uniqueness theorems up to unitary conjugacy for unital, full and nuclear maps from $A$ into ultraproducts of finite von Neumann factors: any two such maps agreeing on traces and total $K$-theory are unitarily equivalent. There are two consequences. Firstly if one takes the factors to be a sequence $(M_{k_n})_{n}$ of matrix algebras, we obtain a uniqueness result for quasidiagonal approximations of $A$. Secondly, when $(\\mathcal M,\\tau_{\\calM})$ is a II$_1$ factor, a pair $\\phi,\\psi:A\\to\\mathcal M$ of unital, injective and nuclear maps are norm approximately unitarily equivalent if and only if $\\tau_{\\calM}\\circ\\phi=\\tau_{\\calM}\\circ\\psi$.\n The main strategy is to use Schafhauser\u0027s classification of lifts along the trace--kernel extension. Since our codomains may lack the tensorial absorption properties needed in this work, the main new ingredient is a suitable $KK$-uniqueness theorem tailored to our situation. This is inspired by $KK$-uniqueness theorems of Loreaux, Ng and Sutradhar.",
"arxiv_id": "2601.08779",
"authors": [
"Shanshan Hua",
"Stuart White"
],
"categories": [
"math.OA"
],
"license": "http://creativecommons.org/licenses/by/4.0/",
"title": "Uniqueness for embeddings of nuclear $C^*$-algebras into type II$_{1}$ factors",
"url": "https://arxiv.org/abs/2601.08779",
"version": "v1"
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