English

Ubiquity of counterexamples to the Smith-Ward problem

Operator Algebras 2026-07-13 v1 Functional Analysis

Abstract

The Smith-Ward problem about matrix ranges, posed in the 1980s, was recently resolved in the negative by Marcel Scherer (arXiv:2607.04274) by obtaining a three-dimensional operator system SM4(Cr(F2))\mathcal{S} \subseteq M_4(C_r^*(\mathbb{F}_2)) without the lifting property. However, this operator system must be exact. In this paper we show that, for every finitely generated CC^*-algebra A\mathcal{A} without the local lifting property (LLP), there exists a three-dimensional operator system SMn+2(A)\mathcal{S} \subseteq M_{n+2}(\mathcal{A}) without the lifting property (LP), thus generalizing Scherer's result and eliminating the reliance on Ext(A)\text{Ext}(\mathcal{A}) not being a group. In particular, we prove that whenever T\mathcal{T} is a finite-dimensional operator system without the LP, then Mn+2(Cu(T))M_{n+2}(C_u^*(\mathcal{T})) contains a 33-dimensional operator system without the LP for some n2(dim(T)1)n \leq 2(\dim(\mathcal{T})-1). In this way, we yield a plethora of counterexamples to the Smith-Ward problem. In particular, unlike Scherer's example, these three-dimensional operator systems fail both the LP and exactness. We also prove the existence of a three-dimensional operator system that detects nuclearity for unital CC^*-algebras, strengthening previous work of Kavruk (J. Funct. Anal., volume 269, 2015).

Keywords

Cite

@article{arxiv.2607.11001,
  title  = {Ubiquity of counterexamples to the Smith-Ward problem},
  author = {Samuel J. Harris},
  journal= {arXiv preprint arXiv:2607.11001},
  year   = {2026}
}

Comments

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