Search arXivSearch

arXiv · 2302.08028

Computing cohomology groups that classify bundles of strongly self-absorbing $C^*$-algebras

Abstract

Locally trivial bundles of $C^*$-algebras with fibre $D \otimes \mathcal{K}$ for a strongly self-absorbing $C^*$-algebra $D$ over a finite CW-complex $X$ form a group $E^1_D(X)$ that is the first group of a cohomology theory $E^*_D(X)$. In this paper we compute these groups by expressing them in terms of ordinary cohomology and connective $K$-theory. To compare the $C^*$-algebraic version of $gl_1(KU)$ with its classical counterpart we also develop a uniqueness result for the unit spectrum of complex periodic topological $K$-theory.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Marius Dadarlat, James E. McClure, Ulrich Pennig. 2023-02-16. Computing cohomology groups that classify bundles of strongly self-absorbing $C^*$-algebras. https://doi.org/10.1142/s1793525324500110

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

Totally Bounded Elements in W*-probability Spaces

We introduce the notion of a totally ($K$-) bounded element of a $W^*$-probability space $(M, φ)$ and, borrowing ideas of Kadison, give an intrinsic characterization of the $^*$-subalgebra $M_{\operatorname{tb}}$ of totally bounded elements. Namely, we show that $M_{\operatorname{tb}}$ is the unique strongly dense $^*$-subalgebra $M_0$ of totally bounded elements of $M$ for which the collection of totally $1$-bounded elements of $M_0$ is complete with respect to the $\|\cdot\|_φ^\#$-norm and for which $M_0$ is closed under all operators $h_a(\log(Δ))$ for $a \in \mathbb{N}$, where $Δ$ is the modular operator and $h_a(t):=1/\cosh(t-a)$ (see Theorem 4.3). We also prove that totally $K$-bounded elements of an Ocneanu ultraproduct admit representatives with the same total bound using a careful effective estimate of the distance of a given totally bounded element to the totally 1-bounded elements. An alternative proof in the appendix uses an isometric $H^\infty$-lifting theorem for the Ocneanu multiplier quotient, derived from a metric $H^\infty$-lifting theorem for $C^*$-quotients and a $C^*$-algebraic Schur parametrization. We combine these results with Rieffel and Van Daele's bounded operator approach to modular theory to arrive at a new language and axiomatization of $W^*$-probability spaces as metric structures. Previous work of Dabrowski had axiomatized $W^*$-probability spaces using a smeared version of multiplication, but the subalgebra $M_{\operatorname{tb}}$ allows us to give an axiomatization in terms of the original algebra operations. Finally, we prove the (non-)axiomatizability of several classes of $W^*$-probability spaces.

math.OA

Partial factorization and reflexivity of operator algebras

Let $\mathcal{H}$ be a separable infinite dimensional Hilbert space and $\mathcal{B}(\mathcal{H})$ the algebra of all bounded linear operators on $\mathcal{H}$. A subalgebra $\mathfrak{A}$ in $\mathcal{B}(\mathcal{H})$ has the left (resp.\ right) partial factorization property if for any invertible operator $S\in\mathcal{B}(\mathcal{H})$, there exists an isometry (resp.\ a co-isometry) $U\in\mathcal{B}(\mathcal{H})$ such that $U^*S, S^{-1}U\in\mathfrak{A}$. We show that if $\mathfrak{A}$ is weak operator topology closed with the left (resp.\ right) partial factorization property, then $\mathfrak{A}$ is the nest algebra associated with its invariant subspace lattice. In particular, if $\mathfrak{A}$ is transitive, then $\mathfrak{A}=\mathcal{B}(\mathcal{H})$. This gives a positive answer to Question 6.3 raised by B.V.R. Bhat and M. Kumar in \emph{Publ. Res. Inst. Math. Sci.} \textbf{60}(2024), 507--537.

math.OA

C*-irreducible regular inclusions, Galois correspondence and aperiodicity

We characterise C*-irreducible regular C*-inclusions using a number of different conditions considered by different authors. In particular, we show that all C*-irreducible regular inclusions $A\subseteq B$ are modelled by outer Fell bundles $(B_{g})_{g\in G}$ over discrete groups with a simple unit fibre $A=B_1$. In this case, we prove a bijection between intermediate C*-algebras $A\subseteq C \subseteq B$ and subgroups $H$ of $G$. This extends the Galois correspondence for reduced crossed products by discrete group actions established by Cameron-Smith. We relate it to the Galois correspondences of Izumi and Mukohara for fixed-point algebras of actions of compact abelian groups, and the mixed inclusion of a fixed-point algebra in a reduced crossed product considered by Echterhoff-Rørdam. In addition, using a recent result of Geffen-Ursu, we show that the inclusion of a fixed-point subalgebra $A\subseteq B$ of an action of $\mathbb{T}$ or $\mathbb{Z}/p$ for a square-free number $p>0$ is aperiodic if and only if $A$ detects ideals in $B$. We apply this to give examples of C*-irreducible inclusions coming from Cuntz-Pimsner algebras, including crossed products by endomorphisms or transfer operators. In particular, we characterise when a core subalgebra of a graph C*-algebra is C*-irreducible. Lastly, we show that a general regular topologically graded C*-inclusion $A\subseteq B$ is aperiodic and has a unique pseudo-expectation provided $A$ detects ideals in all intermediate C*-algebras of $B$. This partially answers a question by Pitts-Zarikian.

math.OA