A Fejér theorem for boundary quotients arising from algebraic dynamical systems

Fourier analysis for type III representations of the noncommutative torus

For the noncommutative 2-torus, we define and study Fourier transforms arising from representations of states with central supports in the bidual, exhibiting a possibly nontrivial modular structure (i.e. type III representations). We then prove the associated noncommutative analogous of Riemann-Lebesgue Lemma and Hausdorff-Young Theorem. In addition, the $L^p$- convergence result of the Cesaro means (i.e. the Fejer theorem), and the Abel means reproducing the Poisson kernel are also established, providing inversion formulae for the Fourier transforms in $L^p$ spaces, $p\in[1,2]$. Finally, in $…

A locally compact quantum group arising from quantization of the affine group of a local field

Using methods coming from non-formal equivariant quantization, we construct in this short note a unitary dual 2-cocycle on a discrete family of quotient groups of subgroups of the affine group of a local field (which is not of characteristic 2, nor an extension of $\mathbb{Q}_2$). Using results of De Commer about Galois objects in operator algebras, we obtain new examples of locally compact quantum groups in the setting of von Neumann algebras.

The inner structure of boundary quotients of right LCM semigroups

We study distinguished subalgebras and automorphisms of boundary quotients arising from algebraic dynamical systems $(G,P,θ)$. Our work includes a complete solution to the problem of extending Bogolubov automorphisms from the Cuntz algebra in $2 \leq p<\infty$ generators to the $p$-adic ring $C^*$-algebra. For the case where $P$ is abelian and $C^*(G)$ is a maximal abelian subalgebra, we establish a picture for the automorphisms of the boundary quotient that fix $C^*(G)$ pointwise. This allows us to show that they form a maximal abelian subgroup of the entire automorphism group. The picture al…

可分类C* 代数扩张的分类

Classification of Extensions of Classifiable C*-algebras

利用K-理论中的六项正合列以及其特征理想和商的K_0-群的正锥，对某些可分类C* 代数-代数的扩张进行了分类.然后将所得结果应用于一类由置换移位空间产生的C* 代数-代数。

Partial transformation groupoids attached to graphs and semigroups

We introduce the notion of continuous orbit equivalence for partial dynamical systems, and give an equivalent characterization in terms of Cartan-isomorphisms for partial C*-crossed products. Both graph C*-algebras and semigroup C*-algebras can be described as C*-algebras attached to partial dynamical systems. As applications, for graphs, we generalize and explain a result of Matsumoto and Matui relating orbit equivalence and Cartan-isomorphism, and for semigroups, we strengthen several structural results for semigroup C*-algebras concerning amenability, nuclearity as well as simplicity of bou…

紧型的代数量子变换广群

Algebraic quantum transformation groupoids of compact type

本文引入了紧型代数量子变换广群及其离散型对偶，恢复了紧与离散Van Daele代数量子群间的对偶，并提供了源于Fell丛和量子商空间的实例。