scholarly journals Dynamics of compact quantum metric spaces

2020 ◽  
pp. 1-41
Author(s):  
JENS KAAD ◽  
DAVID KYED
Keyword(s):  
Riemannian Manifolds ◽  
Metric Space ◽  
Metric Spaces ◽  
Crossed Product ◽  
Continuous Family ◽  
Isometric Actions ◽  
Crossed Product Algebra ◽  
Product Algebra ◽  
Compact Quantum Metric Space ◽  
Natural Way

We provide a detailed study of actions of the integers on compact quantum metric spaces, which includes general criteria ensuring that the associated crossed product algebra is again a compact quantum metric space in a natural way. Moreover, we provide a flexible set of assumptions ensuring that a continuous family of $\ast$ -automorphisms of a compact quantum metric space yields a field of crossed product algebras which varies continuously in Rieffel’s quantum Gromov–Hausdorff distance. Finally, we show how our results apply to continuous families of Lip-isometric actions on compact quantum metric spaces and to families of diffeomorphisms of compact Riemannian manifolds which vary continuously in the Whitney $C^{1}$ -topology.

CROSSED PRODUCT ORDERS OVER VALUATION RINGS

2001 ◽  
Vol 33 (5) ◽  
pp. 520-526 ◽  
Author(s):  
JOHN S. KAUTA
Keyword(s):  
Crossed Product ◽  
Homological Dimension ◽  
Crossed Products ◽  
Quotient Field ◽  
Group Of Units ◽  
Valuation Rings ◽  
Crossed Product Algebra ◽  
Product Algebra ◽  
Product Order ◽  
Natural Way

Let V be a commutative valuation domain of arbitrary Krull-dimension (rank), with quotient field F, and let K be a finite Galois extension of F with group G, and S the integral closure of V in K. If, in the crossed product algebra K [midast ] G, the 2-cocycle takes values in the group of units of S, then one can form, in a natural way, a ‘crossed product order’ S [midast ] G ⊆ K [midast ] G. In the light of recent results by H. Marubayashi and Z. Yi on the homological dimension of crossed products, this paper discusses necessary and/or sufficient valuation-theoretic conditions, on the extension K/F, for the V-order S [midast ] G to be semihereditary, maximal or Azumaya over V.

scholarly journals KMS states on the crossed product -algebra of a homeomorphism

2021 ◽  
pp. 1-42
Author(s):  
JOHANNES CHRISTENSEN ◽  
KLAUS THOMSEN
Keyword(s):  
Continuous Function ◽  
Ergodic Theory ◽  
Metric Space ◽  
Crossed Product ◽  
Compact Metric Space ◽  
Kms States ◽  
Parameter Group ◽  
Intimate Relation ◽  
Crossed Product Algebra ◽  
Product Algebra

Abstract Let $\phi :X\to X$ be a homeomorphism of a compact metric space X. For any continuous function $F:X\to \mathbb {R}$ there is a one-parameter group $\alpha ^{F}$ of automorphisms (or a flow) on the crossed product $C^*$ -algebra $C(X)\rtimes _{\phi }\mathbb {Z}$ defined such that $\alpha ^{F}_{t}(fU)=fUe^{-itF}$ when $f \in C(X)$ and U is the canonical unitary in the construction of the crossed product. In this paper we study the Kubo--Martin--Schwinger (KMS) states for these flows by developing an intimate relation to the ergodic theory of non-singular transformations and show that the structure of KMS states can be very rich and complicated. Our results are complete concerning the set of possible inverse temperatures; in particular, we show that when $C(X) \rtimes _{\phi } \mathbb Z$ is simple this set is either $\{0\}$ or the whole line $\mathbb R$ .

scholarly journals UNIQUENESS THEOREMS FOR HARMONIC MAPS INTO METRIC SPACES

2002 ◽  
Vol 04 (04) ◽  
pp. 725-750 ◽  
Author(s):  
CHIKAKO MESE
Keyword(s):  
Riemannian Manifolds ◽  
Metric Space ◽  
Metric Spaces ◽  
Harmonic Maps ◽  
Uniqueness Theorems ◽  
Singular Spaces ◽  
Domain Space ◽  
Recent Developments

Recent developments extend much of the known theory of classical harmonic maps between smooth Riemannian manifolds to the case when the target is a metric space of curvature bounded from above. In particular, the existence and regularity theorems for harmonic maps into these singular spaces have been successfully generalized. Furthermore, the uniqueness of harmonic maps is known when the domain has a boundary (with a smallness of image condition if the target curvature is bounded from above by a positive number). In this paper, we will address the question of uniqueness when the domain space is without a boundary in two cases: one, when the curvature of the target is strictly negative and two, for a map between surfaces with nonpositive target curvature.

scholarly journals Semigroups of local homeomorphisms and interaction groups

2007 ◽  
Vol 27 (6) ◽  
pp. 1737-1771 ◽  
Author(s):  
R. EXEL ◽  
J. RENAULT
Keyword(s):  
Compact Space ◽  
Crossed Product ◽  
C Algebra ◽  
Crossed Product Algebra ◽  
Product Algebra

AbstractGiven a semigroup of surjective local homeomorphisms on a compact space X we consider the corresponding semigroup of *-endomorphisms on C(X) and discuss the possibility of extending it to an interaction group, a concept recently introduced by the first named author. We also define a transformation groupoid whose C*-algebra turns out to be isomorphic to the crossed product algebra for the interaction group. Several examples are considered, including one which gives rise to a slightly different construction and should be interpreted as being the C*-algebra of a certain polymorphism.

Certain properties for crossed products by automorphisms with a certain non-simple tracial Rokhlin property

2012 ◽  
Vol 33 (5) ◽  
pp. 1391-1400 ◽  
Author(s):  
XIAOCHUN FANG ◽  
QINGZHAI FAN
Keyword(s):  
Finite Group ◽  
Crossed Product ◽  
Crossed Products ◽  
Infinite Dimensional ◽  
Crossed Product Algebra ◽  
A Finite Group ◽  
Product Algebra ◽  
Tracial Rokhlin Property

AbstractLet $\Omega $ be a class of unital $C^*$-algebras. Then any simple unital $C^*$-algebra $A\in \mathrm {TA}(\mathrm {TA}\Omega )$ is a $\mathrm {TA}\Omega $ algebra. Let $A\in \mathrm {TA}\Omega $ be an infinite-dimensional $\alpha $-simple unital $C^*$-algebra with the property SP. Suppose that $\alpha :G\to \mathrm {Aut}(A)$ is an action of a finite group $G$ on $A$ which has a certain non-simple tracial Rokhlin property. Then the crossed product algebra $C^*(G,A,\alpha )$ belongs to $\mathrm {TA}\Omega $.

FREE-PRODUCT GROUPS, CUNTZ-KRIEGER ALGEBRAS, AND COVARIANT MAPS

1991 ◽  
Vol 02 (04) ◽  
pp. 457-476 ◽  
Author(s):  
JOHN SPIELBERG
Keyword(s):  
Free Product ◽  
Compact Convex ◽  
Negative Answer ◽  
Crossed Product ◽  
Crossed Products ◽  
Explicit Computation ◽  
Completely Positive ◽  
Cyclic Groups ◽  
Crossed Product Algebra ◽  
Product Algebra

A construction is given relating a finitely generated free-product of cyclic groups with a certain Cuntz-Krieger algebra, generalizing the relation between the Choi algebra and 02. It is shown that a certain boundary action of such a group yields a Cuntz-Krieger algebra by the crossed-product construction. Certain compact convex spaces of completely positive mappings associated to a crossed-product algebra are introduced. These are used to generalize a problem of J. Anderson regarding the representation theory of the Choi algebra. An explicit computation of these spaces for the crossed products under study yields a negative answer to this problem.

scholarly journals PTOLEMAIC SPACES AND CAT(0)

2009 ◽  
Vol 51 (2) ◽  
pp. 301-314 ◽  
Author(s):  
S. M. BUCKLEY ◽  
K. FALK ◽  
D. J. WRAITH
Keyword(s):  
Euclidean Space ◽  
Riemannian Manifolds ◽  
Metric Space ◽  
Metric Spaces ◽  
Finsler Manifold ◽  
Full Generality ◽  
Space Setting ◽  
Ptolemaic Space

AbstractWe consider Ptolemy's inequality in a metric space setting. It is not hard to see that CAT(0) spaces satisfy this inequality. Although the converse is not true in full generality, we show that if our Ptolemaic space is either a Riemannian or Finsler manifold, then it must also be CAT(0). Ptolemy's inequality is closely related to inversions of metric spaces. We exploit this link to establish a new characterization of Euclidean space amongst all Riemannian manifolds.

scholarly journals The block Schur product is a Hadamard product

2020 ◽  
Vol 126 (3) ◽  
pp. 603-616
Author(s):  
Erik Christensen
Keyword(s):  
Fourier Coefficients ◽  
Hadamard Product ◽  
Natural Generalization ◽  
Continuous Functions ◽  
Crossed Product ◽  
Convolution Product ◽  
C Algebra ◽  
Schur Product ◽  
Crossed Product Algebra ◽  
Product Algebra

Given two $n \times n $ matrices $A = (a_{ij})$ and $B=(b_{ij}) $ with entries in $B(H)$ for some Hilbert space $H$, their block Schur product is the $n \times n$ matrix $ A\square B := (a_{ij}b_{ij})$. Given two continuous functions $f$ and $g$ on the torus with Fourier coefficients $(f_n)$ and $(g_n)$ their convolution product $f \star g$ has Fourier coefficients $(f_n g_n)$. Based on this, the Schur product on scalar matrices is also known as the Hadamard product. We show that for a C*-algebra $\mathcal{A} $, and a discrete group $G$ with an action $\alpha _g$ of $G$ on $\mathcal{A} $ by *-automorphisms, the reduced crossed product C*-algebra $\mathrm {C}^*_r(\mathcal{A} , \alpha , G)$ possesses a natural generalization of the convolution product, which we suggest should be named the Hadamard product. We show that this product has a natural Stinespring representation and we lift some known results on block Schur products to this setting, but we also show that the block Schur product is a special case of the Hadamard product in a crossed product algebra.

scholarly journals On the gluing of hyperconvex metrics and diversities

2014 ◽  
Vol 13 (1) ◽  
pp. 65-76 ◽  
Author(s):  
Bożena Piątek
Keyword(s):  
Metric Space ◽  
Metric Spaces ◽  
Nonempty Intersection ◽  
Natural Way

AbstractIn this work we consider two hyperconvex diversities (or hyperconvex metric spaces) (X, δX) and (Y, δY) with nonempty intersection and we wonder whether there is a natural way to glue them so that the new glued diversity (or metric space) remains being hyperconvex. We provide positive and negative answers in both situations.

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