scholarly journals Characteristic invatiant of tensor product actions and actions on crossed products

2002 ◽  
Vol 73 (3) ◽  
pp. 357-376
Author(s):  
Yukako Miwa ◽  
Yoshikazu Katayama
Keyword(s):  
Tensor Product ◽  
Discrete Group ◽  
Product Formula ◽  
Crossed Product ◽  
Crossed Products ◽  
Modular Invariant ◽  
Characteristic Invariant ◽  
Extended Action ◽  
Product Action

AbstractThe first purpose of this paper is to give a tensor product formula of the characteristic invariant and modular invariant for a tensor product action of a discrete group G on AFD factors. The second purpose is to describe a characteristic invariant and modular invariant of the extended action to a crossed product in terms of the original invariants.

scholarly journals TENSOR-PRODUCT COACTION FUNCTORS

2020 ◽  
pp. 1-16
Author(s):  
S. KALISZEWSKI ◽  
MAGNUS B. LANDSTAD ◽  
JOHN QUIGG
Keyword(s):  
Tensor Product ◽  
Recent Work ◽  
Analogous Result ◽  
Crossed Product ◽  
Discrete Groups ◽  
Crossed Products ◽  
Fixed Action ◽  
Product Action ◽  
K Theory

Recent work by Baum et al. [‘Expanders, exact crossed products, and the Baum–Connes conjecture’, Ann. K-Theory 1(2) (2016), 155–208], further developed by Buss et al. [‘Exotic crossed products and the Baum–Connes conjecture’, J. reine angew. Math. 740 (2018), 111–159], introduced a crossed-product functor that involves tensoring an action with a fixed action $(C,\unicode[STIX]{x1D6FE})$ , then forming the image inside the crossed product of the maximal-tensor-product action. For discrete groups, we give an analogue for coaction functors. We prove that composing our tensor-product coaction functor with the full crossed product of an action reproduces their tensor-crossed-product functor. We prove that every such tensor-product coaction functor is exact, and if $(C,\unicode[STIX]{x1D6FE})$ is the action by translation on $\ell ^{\infty }(G)$ , we prove that the associated tensor-product coaction functor is minimal, thereby recovering the analogous result by the above authors. Finally, we discuss the connection with the $E$ -ization functor we defined earlier, where $E$ is a large ideal of $B(G)$ .

scholarly journals Fullness of crossed products of factors by discrete groups

2019 ◽  
Vol 150 (5) ◽  
pp. 2368-2378 ◽  
Author(s):  
Amine Marrakchi
Keyword(s):  
Discrete Group ◽  
Amenable Group ◽  
Complete Characterization ◽  
Crossed Product ◽  
Discrete Groups ◽  
Sufficient Condition ◽  
Crossed Products ◽  
Product Factor ◽  
Jones Criterion ◽  
Arbitrary Factor

AbstractLet M be an arbitrary factor and $\sigma : \Gamma \curvearrowright M$ an action of a discrete group. In this paper, we study the fullness of the crossed product $M \rtimes _\sigma \Gamma $. When Γ is amenable, we obtain a complete characterization: the crossed product factor $M \rtimes _\sigma \Gamma $ is full if and only if M is full and the quotient map $\overline {\sigma } : \Gamma \rightarrow {\rm out}(M)$ has finite kernel and discrete image. This answers the question of Jones from [11]. When M is full and Γ is arbitrary, we give a sufficient condition for $M \rtimes _\sigma \Gamma $ to be full which generalizes both Jones' criterion and Choda's criterion. In particular, we show that if M is any full factor (possibly of type III) and Γ is a non-inner amenable group, then the crossed product $M \rtimes _\sigma \Gamma $ is full.

scholarly journals Spectral triples on irreversible C∗-dynamical systems

2021 ◽  
Author(s):  
Valeriano Aiello ◽  
Daniele Guido ◽  
Tommaso Isola
Keyword(s):  
Dynamical Systems ◽  
Product Formula ◽  
Crossed Product ◽  
Spectral Triple ◽  
Crossed Products ◽  
Spectral Triples ◽  
Main Assumption ◽  
Noncommutative Spaces ◽  
Covering Projection ◽  
Injective Endomorphism

Given a spectral triple on a [Formula: see text]-algebra [Formula: see text] together with a unital injective endomorphism [Formula: see text], the problem of defining a suitable crossed product [Formula: see text]-algebra endowed with a spectral triple is addressed. The proposed construction is mainly based on the works of Cuntz and [A. Hawkins, A. Skalski, S. White and J. Zacharias, On spectral triples on crossed products arising from equicontinuous actions, Math. Scand. 113(2) (2013) 262–291], and on our previous papers [V. Aiello, D. Guido and T. Isola, Spectral triples for noncommutative solenoidal spaces from self-coverings, J. Math. Anal. Appl. 448(2) (2017) 1378–1412; V. Aiello, D. Guido and T. Isola, A spectral triple for a solenoid based on the Sierpinski gasket, SIGMA Symmetry Integrability Geom. Methods Appl. 17(20) (2021) 21]. The embedding of [Formula: see text] in [Formula: see text] can be considered as the dual form of a covering projection between noncommutative spaces. A main assumption is the expansiveness of the endomorphism, which takes the form of the local isometricity of the covering projection, and is expressed via the compatibility of the Lip-norms on [Formula: see text] and [Formula: see text].

scholarly journals On maximal ideals in certain reduced twisted C*-crossed products

2015 ◽  
Vol 158 (3) ◽  
pp. 399-417 ◽  
Author(s):  
ERIK BÉDOS ◽  
ROBERTO CONTI
Keyword(s):  
Discrete Group ◽  
Crossed Product ◽  
Crossed Products ◽  
Bijective Correspondence ◽  
C Algebra ◽  
Maximal Ideals ◽  
Maximal Invariant

AbstractWe consider a twisted action of a discrete groupGon a unital C*-algebraAand give conditions ensuring that there is a bijective correspondence between the maximal invariant ideals ofAand the maximal ideals in the associated reduced C*-crossed product.

scholarly journals Contractive Spectral Triples for Crossed Products

2014 ◽  
Vol 114 (2) ◽  
pp. 275 ◽  
Author(s):  
Alan L. T. Paterson
Keyword(s):  
Coding Theory ◽  
Duality Theorem ◽  
Discrete Group ◽  
Crossed Product ◽  
Contractive Condition ◽  
Crossed Products ◽  
Isometric Condition ◽  
Spectral Triples ◽  
Groups Of Diffeomorphisms ◽  
Discrete Group Action

Connes showed that spectral triples encode (noncommutative) metric information. Further, Connes and Moscovici in their metric bundle construction showed that, as with the Takesaki duality theorem, forming a crossed product spectral triple can substantially simplify the structure. In a recent paper, Bellissard, Marcolli and Reihani (among other things) studied in depth metric notions for spectral triples and crossed product spectral triples for $Z$-actions, with applications in number theory and coding theory. In the work of Connes and Moscovici, crossed products involving groups of diffeomorphisms and even of étale groupoids are required. With this motivation, the present paper develops part of the Bellissard-Marcolli-Reihani theory for a general discrete group action, and in particular, introduces coaction spectral triples and their associated metric notions. The isometric condition is replaced by the contractive condition.

scholarly journals Iterated crossed products

2014 ◽  
Vol 13 (07) ◽  
pp. 1450036 ◽  
Author(s):  
Florin Panaite
Keyword(s):  
Tensor Product ◽  
Crossed Product ◽  
Smash Product ◽  
Algebra Structure ◽  
Crossed Products ◽  
Twisted Tensor Product

We define a "mirror version" of Brzeziński's crossed product and we prove that, under certain circumstances, a Brzeziński crossed product D ⊗R,σ V and a mirror version [Formula: see text] may be iterated, obtaining an algebra structure on W ⊗ D ⊗ V. Particular cases of this construction are the iterated twisted tensor product of algebras and the quasi-Hopf two-sided smash product.

scholarly journals Strong pure infiniteness of crossed products

2016 ◽  
Vol 38 (1) ◽  
pp. 220-243
Author(s):  
E. KIRCHBERG ◽  
A. SIERAKOWSKI
Keyword(s):  
Discrete Group ◽  
Closed Ideal ◽  
Crossed Product ◽  
General Criterion ◽  
Crossed Products ◽  
Compact Sets ◽  
Compact Spaces ◽  
Is Element ◽  
Contraction Property ◽  
Disjoint Sets

Consider an exact action of a discrete group $G$ on a separable C*-algebra $A$. It is shown that the reduced crossed product $A\rtimes _{\unicode[STIX]{x1D70E},\unicode[STIX]{x1D706}}G$ is strongly purely infinite—provided that the action of $G$ on any quotient $A/I$ by a $G$-invariant closed ideal $I\neq A$ is element-wise properly outer and that the action of $G$ on $A$ is $G$-separating (cf. Definition 5.1). This is the first non-trivial sufficient general criterion for strong pure infiniteness of reduced crossed products of C*-algebras $A$ that are not $G$-simple. In the case $A=\text{C}_{0}(X)$, the notion of a $G$-separating action corresponds to the property that two compact sets $C_{1}$ and $C_{2}$, that are contained in open subsets $C_{j}\subseteq U_{j}\subseteq X$, can be mapped by elements $g_{1},g_{2}$ of $G$ onto disjoint sets $\unicode[STIX]{x1D70E}_{g_{j}}(C_{j})\subseteq U_{j}$, but satisfy not necessarily the contraction property $\unicode[STIX]{x1D70E}_{g_{j}}(U_{j})\subseteq \overline{U_{j}}$. A generalization of strong boundary actions on compact spaces to non-unital and non-commutative C*-algebras $A$ (cf. Definition 7.1) is also introduced. It is stronger than the notion of $G$-separating actions by Proposition 7.6, because $G$-separation does not imply $G$-simplicity and there are examples of $G$-separating actions with reduced crossed products that are stably projection-less and non-simple.

scholarly journals CROSSED PRODUCTS BY ENDOMORPHISMS, VECTOR BUNDLES AND GROUP DUALITY

2005 ◽  
Vol 16 (02) ◽  
pp. 137-171 ◽  
Author(s):  
EZIO VASSELLI
Keyword(s):  
Vector Bundle ◽  
Vector Bundles ◽  
Product Formula ◽  
Crossed Product ◽  
Crossed Products ◽  
General Group

We construct the crossed product [Formula: see text] of a C(X)-algebra [Formula: see text] by an endomorphism ρ, in such a way that ρ becomes induced by the bimodule [Formula: see text] of continuous sections of a vector bundle ℰ → X. Some motivating examples for such a construction are given. Furthermore, we study the C*-algebra of G-invariant elements of the Cuntz-Pimsner algebra [Formula: see text] associated with [Formula: see text], where G is a (noncompact, in general) group acting on ℰ. In particular, the C*-algebra of invariant elements with respect to the action of the group of special unitaries of ℰ is a crossed product in the above sense. We also study the analogous construction on certain Hilbert bimodules, called "noncommutative pullbacks".

A Galois Correspondence for Reduced Crossed Products of Simple -algebras by Discrete Groups

2019 ◽  
Vol 71 (5) ◽  
pp. 1103-1125 ◽  
Author(s):  
Jan Cameron ◽  
Roger R. Smith
Keyword(s):  
Dynamical System ◽  
Discrete Group ◽  
Crossed Product ◽  
Discrete Groups ◽  
Crossed Products ◽  
Outer Automorphisms ◽  
Galois Correspondence ◽  
Simple Algebras ◽  
Unital Simple

AbstractLet a discrete group $G$ act on a unital simple $\text{C}^{\ast }$-algebra $A$ by outer automorphisms. We establish a Galois correspondence $H\mapsto A\rtimes _{\unicode[STIX]{x1D6FC},r}H$ between subgroups of $G$ and $\text{C}^{\ast }$-algebras $B$ satisfying $A\subseteq B\subseteq A\rtimes _{\unicode[STIX]{x1D6FC},r}G$, where $A\rtimes _{\unicode[STIX]{x1D6FC},r}G$ denotes the reduced crossed product. For a twisted dynamical system $(A,G,\unicode[STIX]{x1D6FC},\unicode[STIX]{x1D70E})$, we also prove the corresponding result for the reduced twisted crossed product $A\rtimes _{\unicode[STIX]{x1D6FC},r}^{\unicode[STIX]{x1D70E}}G$.

scholarly journals Strong Morita equivalence for inclusions of $C^*$-algebras induced by twisted actions of a countable discrete group

2021 ◽  
Vol 127 (2) ◽  
pp. 317-336
Author(s):  
Kazunori Kodaka
Keyword(s):  
Discrete Group ◽  
Morita Equivalence ◽  
Crossed Product ◽  
Crossed Products ◽  
C Algebra ◽  
C Algebras ◽  
Morita Equivalent ◽  
Countable Discrete Group ◽  
Relative Commutant ◽  
Strong Morita Equivalence

We consider two twisted actions of a countable discrete group on $\sigma$-unital $C^*$-algebras. Then by taking the reduced crossed products, we get two inclusions of $C^*$-algebras. We suppose that they are strongly Morita equivalent as inclusions of $C^*$-algebras. Also, we suppose that one of the inclusions of $C^*$-algebras is irreducible, that is, the relative commutant of one of the $\sigma$-unital $C^*$-algebra in the multiplier $C^*$-algebra of the reduced twisted crossed product is trivial. We show that the two actions are then strongly Morita equivalent up to some automorphism of the group.

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