Property T and Amenable Transformation Group C*-algebras

2015 ◽  
Vol 58 (1) ◽  
pp. 110-114 ◽  
Author(s):  
F. Kamalov
Keyword(s):  
Compact Hausdorff Space ◽  
Discrete Group ◽  
Hausdorff Space ◽  
Transformation Group ◽  
Amenable Group ◽  
Transformation Groups ◽  
C Algebra ◽  
C Algebras ◽  
Property T ◽  
Tracial States

AbstractIt is well known that a discrete group that is both amenable and has Kazhdan’s Property T must be finite. In this note we generalize this statement to the case of transformation groups. We show that if G is a discrete amenable group acting on a compact Hausdorff space X, then the transformation group C*-algebra C*(X; G) has Property T if and only if both X and G are finite. Our approach does not rely on the use of tracial states on C*(X; G).

Property T for general C*-algebras

2013 ◽  
Vol 156 (2) ◽  
pp. 229-239 ◽  
Author(s):  
CHI–KEUNG NG
Keyword(s):  
Compact Hausdorff Space ◽  
Hausdorff Space ◽  
Locally Compact Groups ◽  
Compact Groups ◽  
Locally Compact ◽  
C Algebras ◽  
Strong Property ◽  
Property T ◽  
Definition Of ◽  
Locally Compact Hausdorff Space

AbstractIn this paper, we extend the definition of property T and strong property T to general C*-algebras (not necessarily unital). We show that if an inclusion pair of locally compact groups (G,H) has property T, then (C*(G), C*(H)) has property T. As a partial converse, if T is abelian and C*(G) has property T, then T is compact. We also show that if Ω is a first countable locally compact Hausdorff space, then C0(Ω) has (strong) property T if and only if Ω is discrete. Furthermore, the non-unital C*-algebra $c_0(\mathbb{Z}^n)\rtimes SL_n(\mathbb{Z})$ has strong property T when n ≥ 3. We also give some equivalent forms of strong property T, which are new even in the unital case.

scholarly journals Dynamical complexity and K-theory of Lp operator crossed products

2019 ◽  
pp. 1-33
Author(s):  
Yeong Chyuan Chung
Keyword(s):  
Compact Hausdorff Space ◽  
Discrete Group ◽  
Hausdorff Space ◽  
Crossed Products ◽  
Dynamical Complexity ◽  
Countable Discrete Group ◽  
K Theory ◽  
Assembly Map

We apply quantitative (or controlled) [Formula: see text]-theory to prove that a certain [Formula: see text] assembly map is an isomorphism for [Formula: see text] when an action of a countable discrete group [Formula: see text] on a compact Hausdorff space [Formula: see text] has finite dynamical complexity. When [Formula: see text], this is a model for the Baum–Connes assembly map for [Formula: see text] with coefficients in [Formula: see text], and was shown to be an isomorphism by Guentner et al.

The Primitive Ideal Space of a C*-Algebra

1974 ◽  
Vol 26 (1) ◽  
pp. 42-49 ◽  
Author(s):  
John Dauns
Keyword(s):  
Compact Hausdorff Space ◽  
Hausdorff Space ◽  
Complete Characterization ◽  
Primitive Ideal ◽  
Ideal Space ◽  
Compact Sets ◽  
Locally Compact ◽  
C Algebra ◽  
Weak Star ◽  
Locally Compact Hausdorff Space

The commutative Gelfand-Naimark Theorem says that any commutative C*-algebra A is isomorphic to the ring C0(M, C) of all continuous complex-valued functions tending to zero outside of compact sets of a locally compact Hausdorff space M. A very important part of this theorem is an intrinsic and also a complete characterization of M as exactly the primitive ideal space of A in the hull-kernel (or weak-star) topology. In the non-commutative case, A ≌ Γ0(M, E)—the ring of sections tending to zero outside of compact subsets of a locally compact Hausdorff space M with values in the stalks or fibers E.

QUANTIZATION AND SUPERSELECTION SECTORS I: TRANSFORMATION GROUP C*-ALGEBRAS

1990 ◽  
Vol 02 (01) ◽  
pp. 45-72 ◽  
Author(s):  
N.P. LANDSMAN
Keyword(s):  
Irreducible Representation ◽  
Large Class ◽  
Configuration Space ◽  
Topological Charge ◽  
Transformation Group ◽  
Irreducible Representations ◽  
Locally Compact ◽  
C Algebra ◽  
C Algebras ◽  
Charge Quantization

Quantization is defined as the act of assigning an appropriate C*-algebra [Formula: see text] to a given configuration space Q, along with a prescription mapping self-adjoint elements of [Formula: see text] into physically interpretable observables. This procedure is adopted to solve the problem of quantizing a particle moving on a homogeneous locally compact configuration space Q=G/H. Here [Formula: see text] is chosen to be the transformation group C*-algebra corresponding to the canonical action of G on Q. The structure of these algebras and their representations are examined in some detail. Inequivalent quantizations are identified with inequivalent irreducible representations of the C*-algebra corresponding to the system, hence with its superselection sectors. Introducing the concept of a pre-Hamiltonian, we construct a large class of G-invariant time-evolutions on these algebras, and find the Hamiltonians implementing these time-evolutions in each irreducible representation of [Formula: see text]. “Topological” terms in the Hamiltonian (or the corresponding action) turn out to be representation-dependent, and are automatically induced by the quantization procedure. Known “topological” charge quantization or periodicity conditions are then identically satisfied as a consequence of the representation theory of [Formula: see text].

CAPACITIES ON C*-ALGEBRAS

2003 ◽  
Vol 06 (03) ◽  
pp. 373-388
Author(s):  
HENRI COMMAN
Keyword(s):  
Hausdorff Space ◽  
Large Deviation ◽  
Radon Measures ◽  
C Algebra ◽  
C Algebras ◽  
Upper Semicontinuous ◽  
Large Deviations Theory ◽  
Noncommutative Version ◽  
Compactness Theorems ◽  
Locally Compact Hausdorff Space

We distinguish three classes of capacities on a C*-algebra: subadditive, additive and maxitive. A tightness notion for capacities, the vague and narrow topologies on the set of capacities are introduced. The vague space of additive capacities which are finite on compact projections is a noncommutative version of the usual vague space of Radon measures on a locally compact Hausdorff space X. We give criterions of vague and narrow relative compactness in various classes of capacities. This allows us to extend most classical compactness theorems for Radon measures. The set of bounded (resp. tight) maxitive capacities is in bijection with the set of positive q-upper semicontinuous (resp. strongly q-upper semicontinuous) operators. This allows us to define a vague (resp. narrow) large deviation principle for a net of capacities as a vague (resp. narrow) convergence of this net towards a maxitive capacity, generalizing the classical notion for Radon probability measures on X. Next, we apply compactness theorems in order to extend some results in large deviations theory.

On $C^*$-algebras associated to actions of discrete subgroups of $\operatorname{SL}(2,\mathbb{R})$ on the punctured plane

2020 ◽  
Vol 126 (3) ◽  
pp. 540-558
Author(s):  
Jacopo Bassi
Keyword(s):  
Homogeneous Space ◽  
Transformation Group ◽  
Matrix Multiplication ◽  
Crossed Products ◽  
Discrete Subgroups ◽  
Horocycle Flow ◽  
Discrete Transformation ◽  
Compact Homogeneous Space ◽  
C Algebra ◽  
C Algebras

Dynamical conditions that guarantee stability for discrete transformation group $C^*$-algebras are determined. The results are applied to the case of some discrete subgroups of $\operatorname{SL} (2,\mathbb{R} )$ acting on the punctured plane by means of matrix multiplication of vectors. In the case of cocompact subgroups, further properties of such crossed products are deduced from properties of the $C^*$-algebra associated to the horocycle flow on the corresponding compact homogeneous space of $\operatorname{SL} (2,\mathbb{R} )$.

HYPERREFLEXIVITY CONSTANTS OF THE BOUNDED -COCYCLE SPACES OF GROUP ALGEBRAS AND C*-ALGEBRAS

2019 ◽  
Vol 109 (1) ◽  
pp. 112-130
Author(s):  
EBRAHIM SAMEI ◽  
JAFAR SOLTANI FARSANI
Keyword(s):  
Polynomial Growth ◽  
Banach Algebras ◽  
Amenable Group ◽  
Open Subgroup ◽  
Group Algebras ◽  
Convolution Operators ◽  
Locally Compact ◽  
C Algebra ◽  
C Algebras ◽  
Strong Property

We introduce the concept of strong property $(\mathbb{B})$ with a constant for Banach algebras and, by applying a certain analysis on the Fourier algebra of the unit circle, we show that all C*-algebras and group algebras have the strong property $(\mathbb{B})$ with a constant given by $288\unicode[STIX]{x1D70B}(1+\sqrt{2})$. We then use this result to find a concrete upper bound for the hyperreflexivity constant of ${\mathcal{Z}}^{n}(A,X)$, the space of bounded $n$-cocycles from $A$ into $X$, where $A$ is a C*-algebra or the group algebra of a group with an open subgroup of polynomial growth and $X$ is a Banach $A$-bimodule for which ${\mathcal{H}}^{n+1}(A,X)$ is a Banach space. As another application, we show that for a locally compact amenable group $G$ and $1<p<\infty$, the space $CV_{P}(G)$ of convolution operators on $L^{p}(G)$ is hyperreflexive with a constant given by $384\unicode[STIX]{x1D70B}^{2}(1+\sqrt{2})$. This is the generalization of a well-known result of Christensen [‘Extensions of derivations. II’, Math. Scand. 50(1) (1982), 111–122] for $p=2$.

THE INDEX OF TOEPLITZ OPERATORS ON FREE TRANSFORMATION GROUP C*-ALGEBRAS

2002 ◽  
Vol 34 (1) ◽  
pp. 84-90 ◽  
Author(s):  
EFTON PARK
Keyword(s):  
Vector Bundle ◽  
Differential Operator ◽  
Differential Form ◽  
Compact Manifold ◽  
Toeplitz Operators ◽  
Discrete Group ◽  
Transformation Group ◽  
Hermitian Vector Bundle ◽  
First Order ◽  
C Algebras

Let Γ be a discrete group acting on a compact manifold X, let V be a Γ-equivalent Hermitian vector bundle over X, and let D be a first-order elliptic self-adjoint Γ-equivalent differential operator acting on sections of V. This data is used to define Toeplitz operators with symbols in the transformation group C*-algebra C(X)[rtimes ]Γ, and it is shown that if the symbol of such a Toeplitz operator is invertible, then the operator is Fredholm. In the case where Γ is finite and acts freely on X, a geometric-topological formula for the index is stated that involves an explicitly constructed differential form associated to the symbol.

scholarly journals Weak Containment by Restrictions of Induced Representations

2018 ◽  
Vol 2020 (7) ◽  
pp. 2034-2053
Author(s):  
Matthew Wiersma
Keyword(s):  
Compact Group ◽  
Closed Subgroup ◽  
Discrete Group ◽  
Amenable Group ◽  
Locally Compact Group ◽  
Approximate Identity ◽  
Locally Compact ◽  
Induced Representations ◽  
C Algebras ◽  
Weak Containment

Abstract A QSIN group is a locally compact group G whose group algebra $\mathrm L^{1}(G)$ admits a quasi-central bounded approximate identity. Examples of QSIN groups include every amenable group and every discrete group. It is shown that if G is a QSIN group, H is a closed subgroup of G, and $\pi \!: H\to \mathcal B(\mathcal{H})$ is a unitary representation of H, then $\pi$ is weakly contained in $\Big (\mathrm{Ind}_{H}^{G}\pi \Big )|_{H}$. This provides a powerful tool in studying the C*-algebras of QSIN groups. In particular, it is shown that if G is a QSIN group which contains a copy of $\mathbb{F}_{2}$ as a closed subgroup, then $\mathrm C^{\ast }(G)$ is not locally reflexive and $\mathrm C^{\ast }_{r}(G)$ does not admit the local lifting property. Further applications are drawn to the “(weak) extendability” of Fourier spaces $\mathrm A_{\pi }$ and Fourier–Stieltjes spaces $\mathrm B_{\pi }$.

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