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We investigate the property of commutator-simplicity in algebras from both algebraic and analytic perspectives. We demonstrate that a large class of algebras possess this property. As an analytic analog, we introduce the concept of topological commutator-simplicity for Banach algebras and establish that a σ -unital C ∗ -algebra is topological commutator-simple if and only if its multiplier algebra is. Furthermore, we explore the applications of commutator-simplicity to certain equations involving commutators, emphasizing its relevance in the study of derivations. Specifically, we obtain that every continuous local derivation on L 1 (G , ω) is a derivation when G is a unimodular locally compact group with a diagonal bounded weight ω . [ABSTRACT FROM AUTHOR]

We consider a tracial state on a von Neumann algebra and assume that projections of are independent if . First we present the general criterion of a projection pair independence. We then give a geometric criterion for independence of different pairs of projections. If atoms and are independent then . Also here we deal with an analog of a "symmetric difference" for a pair of projections and , namely, the projection . If , the pairs and are independent then and . If, moreover, and are independent, then and . For an atomless von Neumann algebra a tracial normal state is determined by its specification of independent events. We clarify our considerations with examples of projection pairs with the differemt mutual independency relations. For the full matrix algebra we give several equivalent conditions for the independence of pairs of projections. [ABSTRACT FROM AUTHOR]

We show that if $M\,\bar{\rtimes }_{\unicode[STIX]{x1D6FC}}\,\unicode[STIX]{x1D6E4}$ has the weak Haagerup property, then both $M$ and $\unicode[STIX]{x1D6E4}$ have the weak Haagerup property, and if $\unicode[STIX]{x1D6E4}$ is an amenable group, then the weak Haagerup property of $M$ implies that of $M\,\bar{\rtimes }_{\unicode[STIX]{x1D6FC}}\,\unicode[STIX]{x1D6E4}$. We also give a condition under which the weak Haagerup property for $M$ and $\unicode[STIX]{x1D6E4}$ implies that of $M\,\bar{\rtimes }_{\unicode[STIX]{x1D6FC}}\,\unicode[STIX]{x1D6E4}$. [ABSTRACT FROM AUTHOR]

We define and study the weak Haagerup property for C*-algebras in this article. A C*-algebra with the Haagerup property always has the weak Haagerup property. We prove that a discrete group has the weak Haagerup property if and only if its reduced group C*-algebra also has that property. Moreover, we consider the permanence of the weak Haagerup property under a few canonical constructions of C*-algebras. [ABSTRACT FROM AUTHOR]

Let $\unicode[STIX]{x1D6E4}$ be a countable discrete group that acts on a unital $C^{\ast }$-algebra $A$ through an action $\unicode[STIX]{x1D6FC}$. If $A$ has a faithful $\unicode[STIX]{x1D6FC}$-invariant tracial state $\unicode[STIX]{x1D70F}$, then $\unicode[STIX]{x1D70F}^{\prime }=\unicode[STIX]{x1D70F}\circ {\mathcal{E}}$ is a faithful tracial state of $A\rtimes _{\unicode[STIX]{x1D6FC},r}\unicode[STIX]{x1D6E4}$ where ${\mathcal{E}}:A\rtimes _{\unicode[STIX]{x1D6FC},r}\unicode[STIX]{x1D6E4}\rightarrow A$ is the canonical faithful conditional expectation. We show that $(A\rtimes _{\unicode[STIX]{x1D6FC},r}\unicode[STIX]{x1D6E4},\unicode[STIX]{x1D70F}^{\prime })$ has the Haagerup property if and only if both $(A,\unicode[STIX]{x1D70F})$ and $\unicode[STIX]{x1D6E4}$ have the Haagerup property. As a consequence, suppose that $(A\rtimes _{\unicode[STIX]{x1D6FC},r}\unicode[STIX]{x1D6E4},\unicode[STIX]{x1D70F}^{\prime })$ has the Haagerup property where $\unicode[STIX]{x1D6E4}$ has property $T$ and $A$ has strong property $T$. Then $\unicode[STIX]{x1D6E4}$ is finite and $A$ is residually finite-dimensional. [ABSTRACT FROM PUBLISHER]

We determine the extreme points of the tracial state space of the noncommutative 3-sphere $${C^{\rm alg}(S_{\theta}^{3})}$$ when the deformation parameter θ is an irrational number. [ABSTRACT FROM AUTHOR]

Abstract: We show that Connes'' embedding conjecture on von Neumann algebras is equivalent to the existence of certain algebraic certificates for a polynomial in noncommuting variables to satisfy the following nonnegativity condition: The trace is nonnegative whenever self-adjoint contraction matrices of the same size are substituted for the variables. These algebraic certificates involve sums of hermitian squares and commutators. We prove that they always exist for a similar nonnegativity condition where elements of separable -factors are considered instead of matrices. Under the presence of Connes'' conjecture, we derive degree bounds for the certificates. [Copyright &y& Elsevier]

We give complete descriptions of the tracial states on both the universal and reduced crossed products of a C*-dynamical system consisting of a unital C*-algebra and a discrete group. In particular, we also answer the question of when the tracial states are in canonical bijection with the invariant tracial states on the original C*-algebra. This generalizes the unique trace property for discrete groups. The analysis simplifies greatly in various cases, for example when the conjugacy classes of the original group are all finite, and in other cases gives previously known results, for example when the original C*-algebra is commutative. We also obtain results and examples in the case of abelian groups that contradict existing results in the literature of Bédos and Thomsen. Specifically, we give a finite-dimensional counterexample, and provide a correction to the result of Thomsen. [ABSTRACT FROM AUTHOR]

We introduce a notion of amenable normal extension S of a unital ring R with a finite approximation system F , encompassing the amenable algebras over a field of Gromov and Elek, the twisted crossed product by an amenable group, and the tensor product with a field extension. It is shown that every Sylvester matrix rank function rk of R preserved by S has a canonical extension to a Sylvester matrix rank function rk F for S. In the case of twisted crossed product by an amenable group, and the tensor product with a field extension, it is also shown that rk F depends on rk continuously. When an amenable group has a twisted action on a unital C ⁎ -algebra preserving a tracial state, we also show that two natural Sylvester matrix rank functions on the algebraic twisted crossed product constructed out of the tracial state coincide. [ABSTRACT FROM AUTHOR]