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We define abelian extensions of algebras in congruence-modular varieties. The theory is sufficiently general that it includes, in a natural way, extensions of R-modules for a ring R. We also define a cohomology theory, which we call clone…

Rings and Algebras · Mathematics 2007-05-23 William H. Rowan

We introduce a notion of ``$n$-dual'' to a simplicial vector space for $n\ge 0$. Coming with it, there is a canonical pairing, which we show to be non-degenerate up to homotopy for homotopy $n$-types. As a result this notion of duality is…

Differential Geometry · Mathematics 2025-12-01 Stefano Ronchi , Chenchang Zhu

This paper examines and strengthens the Cuntz-Thomsen picture of equivariant Kasparov theory for arbitrary second-countable locally compact groups, in which elements are given by certain pairs of cocycle representations between C*-dynamical…

Operator Algebras · Mathematics 2025-03-25 James Gabe , Gábor Szabó

Using Godement mean on the Fourier-Stieltjes algebra of a locally compact quantum group we obtain strong separation results for quantum positive-definite functions associated to a subclass of representations, strengthening for example the…

Operator Algebras · Mathematics 2025-01-28 Jacek Krajczok , Adam Skalski

In his seminal paper "Generalized Fixed Point Algebras and Square-Integrable Group Actions", Ralf Meyer showed how to construct generalized fixed-point algebras for $ C^{\ast} $-dynamical systems via their square-integrable representations…

Representation Theory · Mathematics 2017-04-14 Leonard Huang

In this paper, we develop the theory of bimodules over von Neumann algebras, with an emphasis on categorical aspects. We clarify the relationship between dualizability and finite index. We also show that, for von Neumann algebras with…

Operator Algebras · Mathematics 2017-01-23 Arthur Bartels , Christopher L. Douglas , André Henriques

We study extensions of double groupoids in the sense of \cite{AN2} and show some classical results of group theory extensions in the case of double groupoids. For it, given a double groupoid $(\mathcal{B}; \mathcal{V},\mathcal{H};…

K-Theory and Homology · Mathematics 2016-08-25 Jesús Alonso Ochoa Arango , Alejandro Tiraboschi

We will show that group exactness is a von Neumann equivalence invariant. This result generalizes the previously known fact stating that group exactness is invariant under measure equivalence and W*-equivalence.

Operator Algebras · Mathematics 2023-09-06 Bat-Od Battseren

We describe a new approach for classifying conjugacy classes of elementary abelian subgroups in simple algebraic groups over an algebraically closed field, and understanding the normaliser and centraliser structure of these. For toral…

Group Theory · Mathematics 2024-01-29 Jianbei An , Heiko Dietrich , Alastair J. Litterick

Let $G$ be a countable discrete amenable group, ${\cal M}$ a McDuff factor von Neumann algebra, and $A$ a separable nuclear weakly dense C$^*$-subalgebra of ${\cal M}$. We show that if two centrally free actions of $G$ on ${\cal M}$ differ…

Operator Algebras · Mathematics 2011-04-22 Yasuhiko Sato

We prove a weak form of the mean ergodic theorem for actions of amenable locally compact quantum groups in the von Neumann algebra setting.

Operator Algebras · Mathematics 2008-12-05 Rocco Duvenhage

This work provides a generalization of the Gelfand duality to the context of noncommutative locally $C^*$ algebras. Using a reformulation of a theorem proven by Dauns and Hofmann in the 60's we show that every locally $C^*$ algebra can be…

Operator Algebras · Mathematics 2013-07-18 Michael Forger , Daniel V. Paulino

In this paper we discuss the uniqueness of the unitary representations of the non commutative Heisenberg-Weyl algebra. We show that, apart from a critical line for the non commutative position and momentum parameters, the Stone-von Neumann…

Mathematical Physics · Physics 2015-05-13 Laure Gouba , Frederik G. Scholtz

We unify the classic Dauns-Hofmann representation with Kumjian and Renault's Weyl groupoid representation. More precisely, we use ultrafilters to represent C*-algebras with some additional structure on Fell bundles over locally compact…

Operator Algebras · Mathematics 2024-01-30 Tristan Bice

In this paper some applications of the methods and results of its first part and of the results of M. Stone, H. de Vries, P. Roeper are given. In particular: some generalizations of the Stone Duality Theorem are obtained; a completion…

General Topology · Mathematics 2009-08-10 Georgi Dimov

A pseudogroup is a complete infinitely distributive inverse monoid. Such inverse monoids bear the same relationship to classical pseudogroups of transformations as frames do to topological spaces. The goal of this paper is to develop the…

Category Theory · Mathematics 2011-08-08 Mark V. Lawson , Daniel H. Lenz

In this paper we study actions of locally compact quantum groups on von Neumann algebras and prove that every action has a canonical unitary implementation, paralleling Haagerup's classical result on the unitary implementation of a locally…

Operator Algebras · Mathematics 2007-05-23 Stefaan Vaes

Let $R$ be a (not necessary commutative) ring with unit, $d\geq 1$ an integer, and $\lambda$ a unitary character of the additive group $(R,+).$ A pair $(U,V)$ of unitary representations $U$ and $V$ of $R^d$ on a Hilbert space $\mathcal{H}$…

Representation Theory · Mathematics 2025-02-04 Bachir Bekka

Investigating the direct integral decomposition of von Neumann algebras of bounded module operators on self-dual Hilbert W*-moduli an equivalence principle is obtained which connects the theory of direct disintegration of von Neumann…

funct-an · Mathematics 2008-02-03 Michael Frank

We introduce a Hopf algebroid associated to a proper Lie group action on a smooth manifold. We prove that the cyclic cohomology of this Hopf algebroid is equal to the de Rham cohomology of invariant differential forms. When the action is…

Differential Geometry · Mathematics 2010-02-25 Xiang Tang , Yi-Jun Yao , Weiping Zhang
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