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Don Hadwin

Publications and source records attributed to Don Hadwin.

At least 19 recordsLinked to original sources
arXiv2020

Approximate Equivalence in von Neumann Algebras

Suppose $\mathcal{A}$ is a separable unital ASH C*-algebra, $\mathcal{R}$ is a sigma-finite II$_{\infty}$ factor von Neumann algebra, and $\pi,\rho :\mathcal{A}\rightarrow\mathcal{R}$ are unital $\ast$-homomorphisms such that, for every $a\in\mathcal{A}$, the range projections of $\pi\left( a\right) $ and $\rho\left( a\right) $ are Murray von Neuman equivalent in $\mathcal{R}% $. We prove that $\pi$ and $\rho$ are approximately unitarily equivalent modulo $\mathcal{K}_{\mathcal{R}}$, where $\mathcal{K}_{\mathcal{R}}$ is the norm closed ideal generated by the finite projections in $\mathcal{R}$. We also prove a very general result concerning approximate equivalence in arbitrary finite von Neumann algebras.

math.OA↗
arXiv2020

Path-connected Closures of Unitary Orbits

Suppose A and B are unital C*-algebras and A is separable. Let Rep(A,B) denote the set of all unital *-homomorphisms from A to B with the topology of pointwise convergence. We consider the problem of when the closure of the unitary orbit of a single representation in Rep(A,B) is path-connected. An affirmative answer was given by the first author when A is singly generated and B is the algebra of all operators on a separable Hilbert space. We extend this result for all separable A. We also give an affirmative answer when A is AF or homogeneous and B is a von Neumann algebra or when A is ASH and B is a finite von Neumann algebra.

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arXiv2020

Central Sequences in Subhomogeneous Unital C*-algebras

Suppose A is a unital subhomogeneous C*-algebra. We show that every central sequence in A is hypercentral if and only if every pointwise limit of a sequence of irreducible representations is multiplicity free. We also show that every central sequence in A is trivial if and only if every pointwise limit of irreducible representations is irreducible. We also give a nice repesentation of the latter algebras.

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arXiv2019

Nest algebras in an arbitrary vector space

We examine the properties of algebras of linear transformations that leave invariant all subspaces in a totally ordered lattice of subspaces of an arbitrary vector space. We compare our results with those that apply for the corresponding algebras of bounded operators that act on a Hilbert space.

math.RA↗
arXiv2018

A Characterization of Tracially Nuclear C*-algebras

We give two characterizations of tracially nuclear C*-algebras. The first is that the finite summand of the second dual is hyperfinite. The second is in terms of a variant of the weak* uniqueness property. The necessary condition holds for all tracially nuclear C*-algebras. When the algebra is separable, we prove the sufficiency.

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arXiv2018

A Generalized Beurling Theorem in Finite von Neumann Algebras

In 2016 and 2017, Haihui Fan, Don Hadwin and Wenjing Liu proved a commutative and noncommutative version of Beurling's theorems for a continuous unitarily invariant norm $\alpha $ on $L^{\infty}(\mathbb{T},\mu)$ and tracial finite von Neumann algebras $\left( \mathcal{M},\tau \right) $, respectively. In the paper, we study unitarily $\|\|_{1}$-dominating invariant norms $\alpha $ on finite von Neumann algebras. First we get a Burling theorem in commutative von Neumann algebras by defining $H^{\alpha}(\mathbb{T},\mu)=\overline {H^{\infty}(\mathbb{T},\mu)}^{\sigma(L^{\alpha}\left( \mathbb{T} \right),\mathcal{L}^{\alpha^{'}}\left( \mathbb{T} \right))}\cap L^{\alpha}(\mathbb{T},\mu)$, then prove that the generalized Beurling theorem holds. Moreover, we get similar result in noncommutative case. The key ingredients in the proof of our result include a factorization theorem and a density theorem for $L^{\alpha }\left(\mathcal{M},\tau \right) $.

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arXiv2018

Maximal Tracial Algebras

We introduce and study the notion of maximal tracial algebras. We prove several results in a general setting based on dual pairs and multiplier pairs. In a special case that X is a Banach space we determine the abelian subalgebras of B(X) that are maximal tracial for rank-one tensors. We also make slight connections between our ideas and the Kadison Similarity Problem and also the Connes' Embedding Problem.

math.FA↗
arXiv2018

An Extension of the Beurling-Chen-Hadwin-Shen Theorem for Noncommutative Hardy Spaces Associated with Finite von Neumann Algebras

In 2015, Yanni Chen, Don Hadwin and Junhao Shen proved a noncommutative version of Beurling's theorems for a continuous unitarily invariant norm $% \alpha $ on a tracial von Neumann algebra $\left( \mathcal{M},\tau \right) $ where $\alpha $ is $\left\Vert \cdot \right\Vert _{1}$-dominating with respect to $\tau $. In the paper, we first define a class of norms $% N_{\Delta }\left( \mathcal{M},\tau \right) $ on $\mathcal{M}$, called determinant, normalized, unitarily invariant continuous norms on $\mathcal{M}$. If $\alpha \in N_{\Delta }\left( \mathcal{M},\tau \right) $, then there exists a faithful normal tracial state $\rho $ on $\mathcal{M}$ such that $\rho \left( x\right) =\tau \left( xg\right) $ for some positive $g\in L^{1}\left( \mathcal{Z},\tau \right) $ and the determinant of $g$ is positive. For every $\alpha \in N_{\Delta }\left( \mathcal{M},\tau \right) $, we study the noncommutative Hardy spaces $% H^{\alpha }\left( \mathcal{M},\tau \right) $, then prove that the Chen-Hadwin-Shen theorem holds for $L^{\alpha }\left( \mathcal{M},\tau \right) $. The key ingredients in the proof of our result include a factorization theorem and a density theorem for $L^{\alpha }\left( \mathcal{M},\rho \right) $.

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arXiv2018

A note on the Voiculescu's theorem for commutative C$^*$-algebras in semifinite von Neumann algebras

In the current paper, we generalize the "compact operator" part of the Voiculescu's non-commutative Weyl-von Neumann theorem on approximate equivalence of unital $*$-homomorphisms of an commutative C$^*$ algebra $\mathcal{A}$ into a semifinite von Neumann algebra. A result of D. Hadwin for approximate summands of representations into a finite von Neumann factor $\mathcal{R}$ is also extended.

math.OA↗
arXiv2017

Variations of projectivity for C*-algebras

We consider various lifting problems for C*-algebras. As an application of our results we show that any commuting family of order zero maps from matrices to a von Neumann central sequence algebra can be lifted to a commuting family of order zero maps to the C*-central sequence algebra.

math.OA↗
arXiv2017

Stability of group relations under small Hilbert-Schmidt perturbations

If matrices almost satisfying a group relation are close to matrices exactly satisfying the relation, then we say that a group is matricially stable. Here "almost" and "close" are in terms of the Hilbert-Schmidt norm. Using tracial 2-norm on $II_1$-factors we similarly define $II_1$-factor stability for groups. Our main result is that all 1-relator groups with non-trivial center are $II_{1}$-factor stable. Many of them are also matricially stable and RFD. For amenable groups we give a complete characterization of matricial stability in terms of the following approximation property for characters: each character must be a pointwise limit of traces of finite-dimensional representations. This allows us to prove matricial stability for the discrete Heisenberg group $\mathbb H_3$ and for all virtually abelian groups. For non-amenable groups the same approximation property is a necessary condition for being matricially stable. We study this approximation property and show that RF groups with character rigidity have it.

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arXiv2016

An Extension of the Chen-Beurling-Helson-Lowdenslager Theorem

Yanni Chen extended the classical Beurling-Helson-Lowdenslager Theorem for Hardy spaces on the unit circle $\mathbb{T}$ defined in terms of continuous gauge norms on $L^{\infty}$ that dominate $\Vert\cdot\Vert_{1}$. We extend Chen's result to a much larger class of continuous gauge norms. A key ingredient is our result that if $α$ is a continuous normalized gauge norm on $L^{\infty}$, then there is a probability measure $λ$, mutually absolutely continuous with respect to Lebesgue measure on $\mathbb{T}$, such that $α\geq c\Vert\cdot\Vert_{1,λ}$ for some $0<c\leq1.$

math.FA↗
arXiv2016

Topological Orbit Dimension of MF $C^*$-algebras

This paper is a continuation of our work on D. Voiculescu's topological free entropy dimension in unital C*-algebras. In this paper we first prove the topological free entropy dimension of a MF-nuclear and inner QD algebra is irrelevant to its generating family. Then we give the relation between the topological orbit dimension $K_{top}^2$ and the modified free orbit dimension$ K_2^2$ by using MF-traces. We also introduce a new invariant $K_{top}^3$ which is a modification of the topological orbit dimension $K_{top}^2$ when$ K_{top}^2$ is defined. As the applications of $K_{top}^3$, We prove that$ K_{top}^3(A)=0$ if A has property $ c^*-Γ$ and has no finite-dimensional representations. We also give the definition of property MF-c^*-Γ. We then conclude that, for the unital MF $ C^*$-algebra with no finite-dimensional representations, if A has property MF-c*-Γ, then $K_{top}^3(A)=0$.

math.OA↗
arXiv2016

Tracial stability for C*-algebras

We consider tracial stability, which requires that tuples of elements of a C*-algebra with a trace that nearly satisfy the relation are close to tuples that actually satisfy the relation. Here both "near" and "close" are in terms of the associated 2-norm from the trace, e.g., the Hilbert-Schmidt norm for matrices. Precise definitions are stated in terms of liftings from tracial ultraproducts of C*-algebras. We completely characterize matricial tracial stability for nuclear C*-algebras in terms of certain approximation properties for traces. For non-nuclear $C^{\ast}$-algebras we find new obstructions for stability by relating it to Voiculescu's free entropy dimension. We show that the class of C*-algebras that are stable with respect to tracial norms on real-rank-zero C*-algebras is closed under tensoring with commutative C*-algebras. We show that $C(X)$ is tracially stable with respect to tracial norms on all $C^{\ast}$-algebras if and only if $X$ is approximately path-connected.

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arXiv2016

A Beurling Theorem for Generalized Hardy Spaces on a Multiply Connected Domain

The object of this paper is to prove a version of the Beurling-Helson-Lowdenslager invariant subspace theorem for operators on certain Banach spaces of functions on a multiply connected domain in the complex plane. The norms for these spaces are either the usual Lebesgue and Hardy space norms or certain continuous gauge norms. In the Hardy space case the expected corollaries include the characterization of the cyclic vectors as the outer functions in this context, a demonstration that the set of analytic multiplication operators is maximal abelian and reflexive, and a determination of the closed operators that commute with all analytic multiplication operators.

math.FA↗
arXiv2015

A non-commutative Beurling's theorem with respect to unitarily invariant norms

In 1967, Arveson invented a non-commutative generalization of classical $H^{\infty},$ known as finite maximal subdiagonal subalgebras, for a finite von Neumann algebra $\mathcal M$ with a faithful normal tracial state $τ$. In 2008, Blecher and Labuschagne proved a version of Beurling's theorem on $H^\infty$-right invariant subspaces in a non-commutative $L^{p}(\mathcal M,τ)$ space for $1\le p\le \infty$. In the present paper, we define and study a class of norms ${\mathcal{N}}_{c}(\mathcal M, τ)$ on $\mathcal{M},$ called normalized, unitarily invariant, $\Vert \cdot \Vert_{1}$-dominating, continuous norms, which properly contains the class $\{ \Vert \cdot \Vert_{p}:1\leq p< \infty \}.$ For $α\in \mathcal{N}_{c}(\mathcal M, τ),$ we define a non-commutative $L^{α}({\mathcal{M}},τ)$ space and a non-commutative $H^α$ space. Then we obtain a version of the Blecher-Labuschagne-Beurling invariant subspace theorem on $H^\infty$-right invariant subspaces in a non-commutative $L^{α}({\mathcal{M}},τ)$ space. Key ingredients in the proof of our main result include a characterization theorem of $H^α$ and a density theorem for $L^α(\mathcal M,τ)$.

math.OA↗
arXiv2014

A note on unital full amalgamated free products of quasi-diagonal C*-algebras

In the paper, we consider the question whether a unital full amalgamated free product of quasidiagonal C*-algebras is quasidiagonal again. We give a sufficient condition such that a unital full amalgamated free product of quasidiagonal C*-algebras with amalgamation over a finite dimensional C*- algebra is quasidiagonal. Applying this result, we conclude that a unital full free product of two AF algebras with amalgamation over a finite-dimensional C*-algebra is AF if there are faithful tracial states on each of these two AF algebras such that the restrictions on the common subalgebra agree.

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