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B. K. Kwasniewski

Publications and source records attributed to B. K. Kwasniewski.

At least 19 recordsLinked to original sources
arXiv2023

On $C^*$-algebras associated to transfer operators for countable-to-one maps

Our initial data is a transfer operator $L$ for a continuous, countable-to-one map $φ:Δ\to X$ defined on an open subset of a locally compact Hausdorff space $X$. Then $L$ may be identified with a `potential', i.e. a map $\varrho:Δ\to X$ that need not be continuous unless $φ$ is a local homeomorphism. We define the crossed product $C_0(X)\rtimes L$ as a universal $C^*$-algebra with explicit generators and relations, and give an explicit faithful representation of $C_0(X)\rtimes L$ under which it is generated by weighted composition operators. We explain its relationship with Exel-Royer's crossed products, quiver $C^*$-algebras of Muhly and Tomforde, $C^*$-algebras associated to complex or self-similar dynamics by Kajiwara and Watatani, and groupoid $C^*$-algebras associated to Deaconu-Renault groupoids. We describe spectra of core subalgebras of $C_0(X)\rtimes L$ and use it to characterise simplicity of $C_0(X)\rtimes L$ and prove the uniqueness theorem for $C_0(X)\rtimes L$. We give efficient criteria for $C_0(X)\rtimes L$ to be a Kirchberg algebra, and we discuss relationship between KMS states on the core subalgebra of $C_0(X)\rtimes L$ and conformal measures for $φ$.

math.OA↗
arXiv2021

Essential crossed products for inverse semigroup actions: simplicity and pure infiniteness

We study simplicity and pure infiniteness criteria for C*-algebras associated to inverse semigroup actions by Hilbert bimodules and to Fell bundles over etale not necessarily Hausdorff groupoids. Inspired by recent work of Exel and Pitts, we introduce essential crossed products for which there are such criteria. In our approach the major role is played by a generalised expectation with values in the local multiplier algebra. We give a long list of equivalent conditions characterising when the essential and reduced C*-algebras coincide. Our most general simplicity and pure infiniteness criteria apply to aperiodic C*-inclusions equipped with supportive generalised expectations. We thoroughly discuss the relationship between aperiodicity, detection of ideals, purely outer inverse semigroup actions, and non-triviality conditions for dual groupoids.

math.OA↗
arXiv2020

Noncommutative Cartan C*-subalgebras

We characterise Exel's noncommutative Cartan subalgebras in several ways using uniqueness of conditional expectations, relative commutants, or purely outer inverse semigroup actions. We describe in which sense the crossed product decomposition for a noncommutative Cartan subalgebra is unique. We relate the property of being a noncommutative Cartan subalgebra to aperiodic inclusions and effectivity of dual groupoids. In particular, we extend Renault's characterisation of commutative Cartan subalgebras.

math.OA↗
arXiv2019

Variational principles for spectral radius of weighted endomorphisms of $C(X,D)$

We give formulas for the spectral radius of weighted endomorphisms $aα: C(X,D)\to C(X,D)$, $a\in C(X,D)$, where $X$ is a compact Hausdorff space and $D$ is a unital Banach algebra. Under the assumption that $α$ generates a partial dynamical system $(X,φ)$, we establish two kinds of variational principles for $r(aα)$: using linear extensions of $(X,φ)$ and using Lyapunov exponents associated with ergodic measures for $(X,φ)$. This requires considering (twisted) cocycles over $(X,φ)$ with values in an arbitrary Banach algebra $D$, and thus our analysis can not be reduced to any of mutliplicative ergodic theorems known so far. The established variational principles apply not only to weighted endomorphisms but also to a vast class of operators acting on Banach spaces that we call abstract weighted shifts associated with $α: C(X,D)\to C(X,D)$. In particular, they are far reaching generalizations of formulas obtained by Kitover, Lebedev, Latushkin, Stepin and others. They are most efficient when $D=\mathcal{B}(F)$, for a Banach space $F$, and endomorphisms of $\mathcal{B}(F)$ induced by $α$ are inner isometric. As a by product we obtain a dynamical variational principle for an arbitrary operator $b\in \mathcal{B}(F)$ and that it's spectral radius is always a Lyapunov exponent in some direction $v\in F$, when $F$ is reflexive.

math.FA↗
arXiv2019

Topological freeness for $C^*$-correspondences

We study conditions that ensure uniqueness theorems of Cuntz-Krieger type for relative Cuntz-Pimsner algebras $\mathcal{O}(J,X)$ associated to a $C^*$-correspondence $X$ over a $C^*$-algebra $A$. We give general sufficient conditions phrased in terms of a multivalued map $\widehat{X}$ acting on the spectrum $\widehat{A}$ of $A$. When $X(J)$ is of Type I we construct a directed graph dual to $X$ and prove a uniqueness theorem using this graph. When $X(J)$ is liminal, we show that topological freeness of this graph is equivalent to the uniqueness property for $\mathcal{O}(J,X)$, as well as to an algebraic condition, which we call $J$-acyclicity of $X$. As an application we improve the Fowler-Raeburn uniqueness theorem for the Toeplitz algebra $\mathcal{T}_X$. We give new simplicity criteria for $\mathcal{O}_X$. We generalize and enhance uniqueness results for relative quiver $C^*$-algebras of Muhly and Tomforde. We also discuss applications to crossed products by endomorphisms.

math.OA↗
arXiv2016

Crossed products by endomorphisms of $C_0(X)$-algebras

In the first part of the paper, we develop a theory of crossed products of a $C^*$-algebra $A$ by an arbitrary (not necessarily extendible) endomorphism $α:A\to A$. We consider relative crossed products $C^*(A,α;J)$ where $J$ is an ideal in $A$, and describe up to Morita-Rieffel equivalence all gauge invariant ideals in $C^*(A,α;J)$ and give six term exact sequences determining their $K$-theory. We also obtain certain criteria implying that all ideals in $C^*(A,α;J)$ are gauge invariant, and that $C^*(A,α;J)$ is purely infinite. In the second part, we consider a situation where $A$ is a $C_0(X)$-algebra and $α$ is such that $α(f a)=Φ(f)α(a)$, $a\in A$, $f\in C_0(X)$ where $Φ$ is an endomorphism of $C_0(X)$. Pictorially speaking, $α$ is a mixture of a topological dynamical system $(X,φ)$ dual to $(C_0(X),Φ)$ and a continuous field of homomorphisms $α_x$ between the fibers $A(x)$, $x\in X$, of the corresponding $C^*$-bundle. For systems described above, we establish efficient conditions for the uniqueness property, gauge-invariance of all ideals, and pure infiniteness of $C^*(A,α;J)$. We apply these results to the case when $X=$Prim$(A)$ is a Hausdorff space. In particular, if the associated $C^*$-bundle is trivial, we obtain formulas for $K$-groups of all ideals in $C^*(A,α;J)$. In this way, we constitute a large class of crossed products whose ideal structure and $K$-theory is completely described in terms of $(X,φ,\{α_{x}\}_{x\in X};Y)$ where $Y$ is a closed subset of $X$.

math.OA↗
arXiv2015

Cuntz-Krieger uniqueness theorem for crossed products by Hilbert bimodules

It is shown that a C*-algebra generated by any faithful covariant representation of a Hilbert bimodule X is canonically isomorphic to the crossed product associated to X provided that Rieffel's induced representation functor X-ind is topologically free. It is discussed how this result could be applied to universal C*-algebras generated by relations with a circle gauge action. In particular, it leads to generalizations of isomorphism theorems for various crossed products, and is shown to be equivalent to Cuntz-Krieger uniqueness theorem for finite graph C*-algebras (on that occasion an intriguing realization of Cuntz-Krieger algebras as crossed products by Exel's interactions is discovered).

math.OA↗
arXiv2015

Ideal structure of crossed products by endomorphisms via reversible extensions of $C^*$-dynamical systems

We consider an extendible endomorphism $α$ of a $C^*$-algebra $A$. We associate to it a canonical $C^*$-dynamical system $(B,β)$ that extends $(A,α)$ and is `reversible' in the sense that the endomorphism $β$ admits a unique regular transfer operator $β_*$. The theory for $(B,β)$ is analogous to the theory of classic crossed products by automorphisms, and the key idea is to describe the counterparts of classic notions for $(B,β)$ in terms of the initial system $(A,α)$. We apply this idea to study the ideal structure of a non-unital version of the crossed product $C^*(A,α,J)$ introduced recently by the author and A. V. Lebedev. This crossed product depends on the choice of an ideal $J$ in $(\kerα)^\bot$, and if $J=(\kerα)^\bot$ it is a modification of Stacey's crossed product that works well with non-injective $α$'s. We provide descriptions of the lattices of ideals in $C^*(A,α,J)$ consisting of gauge-invariant ideals and ideals generated by their intersection with $A$. We investigate conditions under which these lattices coincide with the set of all ideals in $C^*(A,α,J)$. In particular, we obtain simplicity criteria that besides minimality of the action require either outerness of powers of $α$ or pointwise quasinilpotence of $α$.

math.OA↗
arXiv2013

Topological aperiodicity for product systems over semigroups of Ore type

We prove a version of uniqueness theorem for Cuntz-Pimsner algebras of discrete product systems over semigroups of Ore type. To this end, we introduce Doplicher-Roberts picture of Cuntz-Pimsner algebras, and the semigroup dual to a product system of 'regular' C*-correspondences. Under a certain aperiodicity condition on the latter, we obtain the uniqueness theorem and a simplicity criterion for the algebras in question. These results generalize the corresponding ones for crossed products by discrete groups, due to Archbold and Spielberg, and for Exel's crossed products, due to Exel and Vershik. They also give interesting conditions for topological higher rank graphs and $P$-graphs, and apply to the new Cuntz C*-algebra $\mathcal{Q}_\mathbb{N}$ arising from the "$ax+b$"-semigroup over $\mathbb{N}$.

math.OA↗
arXiv2012

Topological freeness for Hilbert bimodules

It is shown that topological freeness of Rieffel's induced representation functor implies that any $C^*$-algebra generated by a faithful covariant representation of a Hilbert bimodule $X$ over a $C^*$-algebra $A$ is canonically isomorphic to the crossed product $A\rtimes_X \mathbb{Z}$. An ideal lattice description and a simplicity criterion for $A\rtimes_X \mathbb{Z}$ are established.

math.OA↗
arXiv2012

Crossed products by endomorphisms and reduction of relations in relative Cuntz-Pimsner algebras

Starting from an arbitrary endomorphism αof a unital C*-algebra A we construct a crossed product. It is shown that the natural construction depends not only on the C*-dynamical system (A,α) but also on the choice of an ideal orthogonal to kernel of α. The article gives an explicit description of the internal structure of this crossed product and, in particular, discusses the interrelation between relative Cuntz-Pimsner algebras and partial isometric crossed products. We present a canonical procedure that reduces any given C*-correspondence to the 'smallest' C*-correspondence yielding the same relative Cuntz-Pimsner algebra as the initial one. In the context of crossed products this reduction procedure corresponds to the reduction of C*-dynamical systems and allow us to establish a coincidence between relative Cuntz-Pimsner algebras and crossed products introduced.

math.OA↗
arXiv2010

C*-algebras associated with reversible extensions of logistic maps

A construction of reversible extensions of dynamical systems which applies to arbitrary mappings (not necessarily with open range) is presented. It is based on calculating the maximal ideal space of C*-algebras that extends endomorphisms to partial automorphisms via partial isometric representations, and involves a newfound set of "parameters" (the role of parameters play chosen sets or ideals). Additionally, it is characterised as a universal object. As model examples, we give a thorough description of reversible extensions of logistic maps, and a classification of systems associated with compression of unitaries generating homeomorphisms of the circle.

math.DS↗
arXiv2007

Relative Cuntz-Pimsner Algebras, Partial Isometric Crossed Products and Reduction of Relations

The article discusses the interrelation between relative Cuntz-Pimsner algebras and partial isometric crossed products, and presents a procedure that reduces any given Hilbert bimodule to the "smallest" Hilbert bimodule yielding the same relative Cuntz-Pimsner algebra as the initial one. In the context of crossed products this reduction procedure corresponds to reduction of C*-dynamical systems.

math.OA↗
arXiv2007

Crossed product by an arbitrary endomorphism

Starting from an arbitrary endomorphism δof a unital C*-algebra A we construct a crossed product. It is shown that the natural construction depends not only on the C*-dynamical system (A,δ) but also on the choice of an ideal J orthogonal to Ker δ.

math.OA↗
arXiv2006

Covariance algebra of a partial dynamical system

Partial dynamical systems (X,alpha) arise naturally when dealing with commutative C*-dynamical system (A,delta). We associate with every pair (X,alpha), or (A,delta), a covariance C*-algebra C*(X,alpha)=C*(A,delta) which agrees with a partial crossed product - in case alpha is injective, and a crossed product by a monomorphism - in case alpha is onto. The relevance between (X,alpha) and C*(X,alpha) is deeply investigated. In particular, the notions of topological freedom and invariance of a set are generalized, and as a consequence a version of Isomorphism Theorem and a description of ideals of C*(X,alpha) are obtained.

math.OA↗
arXiv2006

Inverse limit systems associated with F_2^n zero schwarzian unimodal mappings

We present an illustrative example of an inverse limit space and a shift map associated with an F_2^n unimodal mapping consisting of two hyperbolae. Topologically, in case n=0 the limit space is an interval, in case n=1,2, it is a sin(1/x)-continuum, and in case n=3 it is a certain continuum endowed with a specific geometrical beauty. The dynamics of the shift map is also described. Operator algebraists may regard the constructed space as a spectrum of a commutative coefficient C*-algebra - an object which plays a role in crossed-product theory.

math.DS↗
arXiv2006

Crossed product of a C*-algebra by a semigroup of bounded positive linear maps. Interactions

The paper presents a construction of the crossed product of a C*-algebra by a commutative semigroup of bounded positive linear maps generated by partial isometries. In particular, it generalizes Antonevich, Bakhtin, Lebedev's crossed product by an endomorphism, and is related to Exel's interactions. One of the main goals is the Isomorphism Theorem established in the case of actions by endomorphisms.

math.OA↗