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This paper is an invitation to Fourier analysis in the context of reduced twisted C*-crossed products associated with discrete unital twisted C*-dynamical systems. We discuss norm-convergence of Fourier series, multipliers and summation…

Operator Algebras · Mathematics 2015-10-20 Erik Bedos , Roberto Conti

It is characterized when coarsening functors between categories of graded modules preserve injectivity of objects, and when they commute with graded covariant Hom functors.

Commutative Algebra · Mathematics 2013-04-09 Fred Rohrer

We prove gauge-invariant uniqueness theorems with respect to maximal and normal coactions for $C^*$-algebras associated to product systems of $C^*$-correspondences. Our techniques of proof are developed in the abstract context of Fell…

Operator Algebras · Mathematics 2012-05-29 S. Kaliszewski , Nadia S. Larsen , John Quigg

Let $G$ and $A$ be objects of a finitely cocomplete homological category $\mathbb C$. We define a notion of an (internal) action of $G$ of $A$ which is functorially equivalent with a point in $\mathbb C$ over $G$, i.e. a split extension in…

Category Theory · Mathematics 2010-03-02 Manfred Hartl , Bruno Loiseau

We prove that the class of principal coactions is closed under one-surjective pullbacks in an appropriate category of algebras equipped with left and right coactions. This allows us to handle cases of C*-algebras lacking two different…

K-Theory and Homology · Mathematics 2013-02-26 Piotr M. Hajac , Elmar Wagner

We propose to define the notion of abstract local cohomology functors. The derived functors of the ordinary local cohomology functor with support in the closed subset defined by an ideal and the generalized local cohomology functor…

Commutative Algebra · Mathematics 2010-01-07 Yuji Yoshino , Takeshi Yoshizawa

We introduce the notion of strong Morita equivalence for group actions on locally C*-algebras and prove that the crossed products associated with two strongly Morita equivalent continuous inverse limit actions of a locally compact group G…

Operator Algebras · Mathematics 2007-10-02 Maria Joita

We consider group actions of topological groups on C*-algebras of the types which occur in many physics models. These are singular actions in the sense that they need not be strongly continuous, or the group need not be locally compact. We…

Operator Algebras · Mathematics 2012-10-16 Hendrik Grundling , Karl-Hermann Neeb

In this paper, we will prove that if $A$ is a $C^*$-algebra with an effective coaction $\epsilon$ by a compact quantum group, then the fixed point algebra and the reduced crossed product are Morita equivalent. As an application, we prove an…

funct-an · Mathematics 2008-02-03 Chi-Keung Ng

In this article we establish the foundations of the Morita homotopy theory of C*-categories. Concretely, we construct a cofibrantly generated simplicial symmetric monoidal Quillen model structure M_Mor on the category C*cat1 of small unital…

Category Theory · Mathematics 2019-10-09 Ivo Dell'Ambrogio , Goncalo Tabuada

Let E be a (right) Hilbert C*-module over a C*-algebra A. If E is equipped with a left action of a second C*-algebra B, then tensor product with E gives rise to a functor from the category of Hilbert B-modules to the category of Hilbert…

Operator Algebras · Mathematics 2016-07-06 Pierre Clare , Tyrone Crisp , Nigel Higson

Given a cocycle on a topological quiver by a locally compact group, the author constructs a skew product topological quiver, and determines conditions under which a topological quiver can be identified as a skew product. We investigate the…

Operator Algebras · Mathematics 2024-11-20 Lucas Hall

We review the notions of a multiplier category and the $W^{*}$-envelope of a $C^{*}$-category. We then consider the notion of an orthogonal sum of a (possibly infinite) family of objects in a $C^{*}$-category. Furthermore, we construct…

K-Theory and Homology · Mathematics 2025-12-11 Ulrich Bunke , Alexander Engel

We show that there is a functor from the category of positive admissible ternary rings to the category of $*$-algebras, which induces an isomorphism of partially ordered sets between the families of $C^*$-norms on the ternary ring and its…

Operator Algebras · Mathematics 2021-08-12 Fernando Abadie , Damián Ferraro

In this note, we show that the category of strongly central series admits co-induced actions, which means that it is Locally Algebraically Cartesian Closed. We also show that some co-induction functors exist in the category of topological…

Group Theory · Mathematics 2018-12-24 Jacques Darné

The notion of a duality between two derived functors as well as an extension theorem for derived functors to larger categories in which they need not be defined is introduced. These ideas are then applied to extend and study the coext…

Rings and Algebras · Mathematics 2014-02-19 Anastasis Kratsios

For a discrete group $G$, we develop a `$G$-balanced tensor product' of two coactions $(A,\delta)$ and $(B,\epsilon)$, which takes place on a certain subalgebra of the maximal tensor product $A\otimes_{\max} B$. Our motivation for this is…

Operator Algebras · Mathematics 2019-12-12 S. Kaliszewski , Magnus B. Landstad , John Quigg

We propose a new approach to study the relation between the module categories of a tilted algebra $C$ and the corresponding cluster-tilted algebra $B=C\ltimes E$. This new approach consists of using the induction functor $-\otimes_C B$ as…

Representation Theory · Mathematics 2016-04-26 Ralf Schiffler , Khrystyna Serhiyenko

The notion of a multiplier of a group X is generalized to that of a C*-multiplier by allowing it to have values in an arbitrary C*-algebra A. On the other hand, the notion of the action of X in A is generalized to that of a projective…

Mathematical Physics · Physics 2007-05-23 Jan Naudts

In this note we recall some recent progress in understanding the representation theory of *-algebras over rings C = R(i) where R is ordered and i^2 = -1. The representation spaces are modules over auxiliary *-algebras with inner products…

Quantum Algebra · Mathematics 2009-01-28 Stefan Waldmann