researchseminars.org

I. G. Todorov (QUB & U. Delaware)
2020-11-06 13:00 - 14:30 UTC | https://stable.researchseminars.org/talk/AthensFAOA/1/
Title: Operator algebraic introduction to non-local games (https://stable.researchseminars.org/talk/AthensFAOA/1/)
by I. G. Todorov (QUB & U. Delaware) as part of Functional analysis and operator algebras in Athens

Abstract: TBA

I. G. Todorov (QUB & U. Delaware)
2020-11-13 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/2/
Title: Operator algebraic introduction to non-local games (2nd talk) (https://stable.researchseminars.org/talk/AthensFAOA/2/)
by I. G. Todorov (QUB & U. Delaware) as part of Functional analysis and operator algebras in Athens

Abstract: TBA

I. G. Todorov (QUB & U. Delaware)
2020-11-20 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/3/
Title: Operator algebraic introduction to non-local games (3rd talk) (https://stable.researchseminars.org/talk/AthensFAOA/3/)
by I. G. Todorov (QUB & U. Delaware) as part of Functional analysis and operator algebras in Athens

Abstract: TBA

I. G. Todorov (QUB & U. Delaware)
2020-11-27 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/4/
Title: Operator algebraic introduction to non-local games (4th talk) (https://stable.researchseminars.org/talk/AthensFAOA/4/)
by I. G. Todorov (QUB & U. Delaware) as part of Functional analysis and operator algebras in Athens

Abstract: TBA

A. Giannopoulos (NKUA)
2020-12-04 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/5/
Title: Isoperimetric constants of metric probability spaces (https://stable.researchseminars.org/talk/AthensFAOA/5/)
by A. Giannopoulos (NKUA) as part of Functional analysis and operator algebras in Athens

Abstract
In this first talk we shall introduce four isoperimetric
constants (the Cheeger constant, the Poincare constant, the exponential concentration
constant and the first moment concentration constant) associated with a Borel
probability measure on R^n and discuss their relation. We shall review classical
results of Maz'ya, Cheeger, Gromov, V. Milman, Buser, Ledoux and others, as well as
a theorem of E. Milman which establishes the equivalence of all four constants in the
log-concave setting.

A. Giannopoulos (NKUA)
2020-12-11 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/6/
Title: Isoperimetric constants of metric probability spaces (2nd talk) (https://stable.researchseminars.org/talk/AthensFAOA/6/)
by A. Giannopoulos (NKUA) as part of Functional analysis and operator algebras in Athens

Abstract: TBA

Kenneth R. Davidson (University of Waterloo)
2020-12-18 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/7/
Title: Noncommutative Choquet theory (NOTE TIME) (https://stable.researchseminars.org/talk/AthensFAOA/7/)
by Kenneth R. Davidson (University of Waterloo) as part of Functional analysis and operator algebras in Athens

Abstract
We introduce a new framework for noncommutative convexity. We develop a
noncommutative Choquet theory and prove an analogue of the Choquet-Bishop-de Leeuw theorem.
This is joint work with Matthew Kennedy.

A. Katavolos (NKUA)
2021-01-08 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/8/
Title: Harmonic Operators and Crossed Products (https://stable.researchseminars.org/talk/AthensFAOA/8/)
by A. Katavolos (NKUA) as part of Functional analysis and operator algebras in Athens

Abstract
We study the space of harmonic operators for a probability measure μ (or a family of measures) on a group G, as a “quantization” of μ-harmonic (or jointly harmonic) functions on G. This leads to two different notions of crossed products of operator spaces by actions of G which coincide when G satisfies a certain approximation property. The corresponding (dual) notions of crossed products of (co-) actions by the von Neumann algebra of G always coincide.This is a survey of joint work with M. Anoussis and I.G. Todorov, and of recent work by D. Andreou.

For Zoom meeting coordinates and additional information see the seminar webpage

http://users.uoa.gr/~akatavol/anak2021.html#1

P. Dodos (NKUA)
2021-01-15 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/9/
Title: High-dimensional random arrays. Structural decompositions and concentration. (https://stable.researchseminars.org/talk/AthensFAOA/9/)
by P. Dodos (NKUA) as part of Functional analysis and operator algebras in Athens

Abstract
A d-dimensional random array is a stochastic process indexed by theset of all d-element subsets of a set I. We shall discuss the structure of finite,high-dimensional random arrays, with finite valued entries (e.g., boolean) whose distribution is sufficiently symmetric.
Specifically, we shall focus on the following interrelated problems: concentration and distributional decompositions.
This is joint work with Kostas Tyros and Petros Valettas

P. Dodos (NKUA)
2021-01-22 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/10/
Title: High-dimensional random arrays. Structural decompositions and concentration. (2nd talk) (https://stable.researchseminars.org/talk/AthensFAOA/10/)
by P. Dodos (NKUA) as part of Functional analysis and operator algebras in Athens

Abstract: TBA

No seminar
2021-01-29 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/11/
by No seminar as part of Functional analysis and operator algebras in Athens

Abstract: TBA

No seminar
2021-02-05 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/12/

No seminar
2021-02-12 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/13/

A. Siskakis (A.U. Thessaloniki)
2021-02-19 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/14/
Title: The Hilbert matrix and its continuous version (https://stable.researchseminars.org/talk/AthensFAOA/14/)
by A. Siskakis (A.U. Thessaloniki) as part of Functional analysis and operator algebras in Athens

Abstract
We will recount some known results on the discrete Hilbert matrix as an operator onspaces of analytic functions, and will consider the continuous version of the operator on suitablefunction spaces. For the latter, a theorem from Abstract Harmonic Analysis will be used todetermine its norm and spectrum.

M. Ghandehari (U. Delaware)
2021-02-26 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/15/
Title: Fourier algebras of the group of R-affine transformations and a dual convolution. (https://stable.researchseminars.org/talk/AthensFAOA/15/)
by M. Ghandehari (U. Delaware) as part of Functional analysis and operator algebras in Athens

Abstract
A major trend in Non-commutative Harmonic Analysis is to investigate function spaces related toFourier analysis (and representation theory) of non-abelian groups. The Fourier algebra, which is associatedwith the left regular representation of the ambient group, is an important example of such function spaces. Thisfunction algebra encodes the properties of the group in various ways; for instance the existence of derivationson this algebra translates into information about the commutativity of the group itself.In this talk, we investigate the Fourier algebra of the group ofR-affine transformations. In particular, wediscuss the non-commutative Fourier transform for this group, and provide an explicit formula for the convolutionproduct on the “dual side” of this transform. As an application of this new dual convolution product, we showan easy dual formulation for (the only known) symmetric derivative on the Fourier algebra of the group.This talk is mainly based on joint articles with Y. Choi.

E. G. Katsoulis (ECU, USA)
2021-03-05 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/16/
Title: Co-universal C*-algebras for product systems (https://stable.researchseminars.org/talk/AthensFAOA/16/)
by E. G. Katsoulis (ECU, USA) as part of Functional analysis and operator algebras in Athens

Abstract
In these talks we will present parts of the recent paper of A. Dor-On, E. Kakariadis, E. Katsoulis, M. Laca with X. Li. The emphasis is on the interaction between selfadjoint and nonselfadjoint operator algebra theory with applications to current problems in C*-algebra theory. Significant effort will be made in carefully reviewing preliminaries, including basic facts from the theory of C*-envelopes and product systems.

Continuous product systems were introduced and studied by Arveson in the late 1980s. The study of their discrete analogues started with the work of Dinh in the 1990s and it was formalized by Fowler in 2002. Discrete product systems are semigroup versions of C*-correspondences, that allow for a joint study of many fundamental C*-algebras, including those which come from C*-correspondences, higher rank graphs and elsewhere.

Katsura’s covariant relations have been proven to give the correct Cuntz-type C*-algebra for a C*-correspondence X. One of the great advantages Katsura’s Cuntz-Pimsner C*-algebra is its co-universality for the class of gauge-compatible injective representations of X. In the late 2000s Carlsen-Larsen-Sims-Vittadello raised the question of the existence of such a co-universal object in the context of product systems. In their work, Carlsen-Larsen-Sims-Vittadello provided an affirmative answer for quasi-lattices, with additional injectivity assumptions on X. The general case has remained open and will be addressed in these talks using tools from non-selfadjoint operator algebra theory.

E. G. Katsoulis (ECU, USA)
2021-03-12 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/17/
Title: Co-universal C*-algebras for product systems, 2nd talk (https://stable.researchseminars.org/talk/AthensFAOA/17/)
by E. G. Katsoulis (ECU, USA) as part of Functional analysis and operator algebras in Athens

Abstract
In these talks we will present parts of the recent paper of A. Dor-On, E. Kakariadis, E. Katsoulis, M. Laca with X. Li. The emphasis is on the interaction between selfadjoint and nonselfadjoint operator algebra theory with applications to current problems in C*-algebra theory. Significant effort will be made in carefully reviewing preliminaries, including basic facts from the theory of C*-envelopes and product systems.

Continuous product systems were introduced and studied by Arveson in the late 1980s. The study of their discrete analogues started with the work of Dinh in the 1990s and it was formalized by Fowler in 2002. Discrete product systems are semigroup versions of C*-correspondences, that allow for a joint study of many fundamental C*-algebras, including those which come from C*-correspondences, higher rank graphs and elsewhere.

Katsura’s covariant relations have been proven to give the correct Cuntz-type C*-algebra for a C*-correspondence X. One of the great advantages Katsura’s Cuntz-Pimsner C*-algebra is its co-universality for the class of gauge-compatible injective representations of X. In the late 2000s Carlsen-Larsen-Sims-Vittadello raised the question of the existence of such a co-universal object in the context of product systems. In their work, Carlsen-Larsen-Sims-Vittadello provided an affirmative answer for quasi-lattices, with additional injectivity assumptions on X. The general case has remained open and will be addressed in these talks using tools from non-selfadjoint operator algebra theory.

E. Kakariadis (Newcastle, UK)
2021-03-19 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/18/
Title: Co-universal C*-algebras for product systems, 3rd talk (https://stable.researchseminars.org/talk/AthensFAOA/18/)
by E. Kakariadis (Newcastle, UK) as part of Functional analysis and operator algebras in Athens

Abstract
In these talks we will present parts of the recent paper of A. Dor-On, E. Kakariadis, E. Katsoulis, M. Laca with X. Li. The emphasis is on the interaction between selfadjoint and nonselfadjoint operator algebra theory with applications to current problems in C*-algebra theory. Significant effort will be made in carefully reviewing preliminaries, including basic facts from the theory of C*-envelopes and product systems.

Continuous product systems were introduced and studied by Arveson in the late 1980s. The study of their discrete analogues started with the work of Dinh in the 1990s and it was formalized by Fowler in 2002. Discrete product systems are semigroup versions of C*-correspondences, that allow for a joint study of many fundamental C*-algebras, including those which come from C*-correspondences, higher rank graphs and elsewhere.

Katsura’s covariant relations have been proven to give the correct Cuntz-type C*-algebra for a C*-correspondence X. One of the great advantages Katsura’s Cuntz-Pimsner C*-algebra is its co-universality for the class of gauge-compatible injective representations of X. In the late 2000s Carlsen-Larsen-Sims-Vittadello raised the question of the existence of such a co-universal object in the context of product systems. In their work, Carlsen-Larsen-Sims-Vittadello provided an affirmative answer for quasi-lattices, with additional injectivity assumptions on X. The general case has remained open and will be addressed in these talks using tools from non-selfadjoint operator algebra theory.

E. Kakariadis (Newcastle, UK)
2021-03-26 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/19/
Title: Co-universal C*-algebras for product systems, 4th talk (https://stable.researchseminars.org/talk/AthensFAOA/19/)
by E. Kakariadis (Newcastle, UK) as part of Functional analysis and operator algebras in Athens

Abstract
In these talks we will present parts of the recent paper of A. Dor-On, E. Kakariadis, E. Katsoulis, M. Laca with X. Li. The emphasis is on the interaction between selfadjoint and nonselfadjoint operator algebra theory with applications to current problems in C*-algebra theory. Significant effort will be made in carefully reviewing preliminaries, including basic facts from the theory of C*-envelopes and product systems.

Continuous product systems were introduced and studied by Arveson in the late 1980s. The study of their discrete analogues started with the work of Dinh in the 1990s and it was formalized by Fowler in 2002. Discrete product systems are semigroup versions of C*-correspondences, that allow for a joint study of many fundamental C*-algebras, including those which come from C*-correspondences, higher rank graphs and elsewhere.

Katsura’s covariant relations have been proven to give the correct Cuntz-type C*-algebra for a C*-correspondence X. One of the great advantages Katsura’s Cuntz-Pimsner C*-algebra is its co-universality for the class of gauge-compatible injective representations of X. In the late 2000s Carlsen-Larsen-Sims-Vittadello raised the question of the existence of such a co-universal object in the context of product systems. In their work, Carlsen-Larsen-Sims-Vittadello provided an affirmative answer for quasi-lattices, with additional injectivity assumptions on X. The general case has remained open and will be addressed in these talks using tools from non-selfadjoint operator algebra theory.

Marcelo Laca (University of Victoria, Canada)
2021-04-02 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/20/
Title: C*-algebras generated by isometries: 60 years and counting (https://stable.researchseminars.org/talk/AthensFAOA/20/)
by Marcelo Laca (University of Victoria, Canada) as part of Functional analysis and operator algebras in Athens

Abstract
The first talk will be a (necessarily biased and partial) survey of the history of
C*-algebras generated by isometries on Hilbert space. I will begin by recalling
classical theorems of Coburn, Douglas, and Cuntz from the 1960’s and 1970’s
and then discuss their proofs. Douglas’ and Cuntz’s approaches already indicate,
in an implicit way, that semigroup crossed products play a central role.
This was not formalized until the late 1980’s and early 1990’s when Murphy,
Stacey, Nica, and then Raeburn and I developed an explicit semigroup crossed
product approach for Toeplitz algebras, focusing on a covariance condition that
works quite well for quasi-lattice ordered groups. I will elaborate a bit on this
approach and show how it works in a few examples. I will finish by discussing
briefly the semigroup C*-algebra C^*_s(P) introduced by Xin Li in the 2010’s
using constructible right ideals to generalize Nica’s covariance condition, and will
finish by giving some non quasi-lattice ordered examples from number theory.

Marcelo Laca (University of Victoria, Canada)
2021-04-09 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/21/
Title: C*-algebras generated by isometries: 60 years and counting (https://stable.researchseminars.org/talk/AthensFAOA/21/)
by Marcelo Laca (University of Victoria, Canada) as part of Functional analysis and operator algebras in Athens

Abstract
The second talk will be on my joint work with Sehnem from the 2020’s about
a universal Toeplitz algebra T_u(P) defined via generators and relations whenever
P is a submonoid of a group G. The C*-algebra T_u(P) coincides with Xin Li’s
C_s^∗(P) when the semigroup satisfies his independence condition but behaves
as expected also when independence fails; for example, it is isomorphic to the
C*-algebra of the left regular representation when the group G is amenable and
also in many nonamenable situations. I will give a characterization of faithful
representations and a uniqueness theorem for these universal Toeplitz algebras,
which are new results even for right LCM monoids. Time permitting I will also
discuss how Sehnem’s covariance algebra of a product system leads to a full
boundary quotient of T_u(P), generalizing the boundary relations of quasi-lattice
orders introduced by Crisp and myself in the 2000’s.

Matthew Kennedy (University of Waterloo, Canada)
2021-04-16 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/22/
Title: Amenability, proximality and higher order syndeticity (https://stable.researchseminars.org/talk/AthensFAOA/22/)
by Matthew Kennedy (University of Waterloo, Canada) as part of Functional analysis and operator algebras in Athens

Abstract
I will present new descriptions of some universal flows associated to a discrete group, obtained using what we view as a kind of “topological Furstenberg correspondence.” The descriptions are algebraic and relatively concrete, involving subsets of the group satisfying a higher order notion of syndeticity. We utilize them to establish new necessary and sufficient conditions for strong amenability and amenability. Furthermore, utilizing similar techniques, we obtain a characterization of “dense orbit sets,” answering a question of Glasner, Tsankov, Weiss and Zucker. Throughout the talk, I will discuss connections to operator algebras.
This is joint work with Sven Raum and Guy Salomon.

For Zoom meeting coordinates
and additional information see the seminar webpage

http://users.uoa.gr/~akatavol/anak2021.html#1

Xin Li (University of Glasgow, UK)
2021-04-23 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/23/
Title: Semigroup C*-algebras and their K-theory (https://stable.researchseminars.org/talk/AthensFAOA/23/)
by Xin Li (University of Glasgow, UK) as part of Functional analysis and operator algebras in Athens

Abstract
I will report on developments in semigroup C*-algebras, with a particular focus on examples, structural properties and classification results. A key ingredient is given by a K-theory formula, which has been generalized recently, as we will discuss.

Matthew Daws (University of Central Lancashire, UK)
2021-05-14 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/24/
Title: Purely infinite algebras and ultrapowers (https://stable.researchseminars.org/talk/AthensFAOA/24/)
by Matthew Daws (University of Central Lancashire, UK) as part of Functional analysis and operator algebras in Athens

Abstract
I will discuss what it means for a Banach Algebra to be purely infinite (with a brief nod towards the important class of purely infinite C*-algebras). The ultrapower construction is an interesting
way to convert "approximate" relations into exact ones, and has
important links to (continuous) model theory. We ask the question:
when does a purely infinite Banach algebra have purely infinite
ultrapowers? This is equivalent to having a "quantified" version of
being purely infinite, where one has norm control over certain
choices. This is always so for C*-algebras, but we present some
examples of Banach algebras where this works, and where it doesn't.
Our examples are rather "natural", in the sense that we don't just
fiddle with the norm of elements. This is joint work with Bence
Horvath.

Sophie Grivaux (Université de Lille, FR)
2021-05-21 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/25/
Title: Typical properties of contractions on l_p spaces (https://stable.researchseminars.org/talk/AthensFAOA/25/)
by Sophie Grivaux (Université de Lille, FR) as part of Functional analysis and operator algebras in Athens

Abstract
Given a separable Banach space $X$ of infinite dimension, one can consider on the space $\mathcal{B}(X)$ of bounded linear operators on $X$ several
natural topologies which turn the closed unit ball $B_1(X)=\{T\in\mathcal{B}(X);||T||\le 1\}$ into a Polish space, i.e. a separable and completely metrizable space.

In this talk, I will present some results concerning typical properties in the Baire Category sense of operators of $B_1(X)$ for these
topologies when $X$ is a $\ell_p$-space, our main interest being to determine whether typical contractions on these spaces have a non-trivial invariant subspace or not.

The talk is based on joint work with \'Etienne Matheron and Quentin Menet.

David Sherman (University of Virginia, USA)
2021-05-28 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/26/
Title: A quantization of coarse structures and uniform Roe algebras (https://stable.researchseminars.org/talk/AthensFAOA/26/)
by David Sherman (University of Virginia, USA) as part of Functional analysis and operator algebras in Athens

Abstract
A coarse structure is a way of talking about "large-scale" properties. It is encoded in a family of relations that often, but not always, come from a metric. A coarse structure naturally gives rise to Hilbert space operators that in turn generate a so-called uniform Roe algebra.
In ongoing work with Bruno Braga and Joe Eisner, we use ideas of Weaver to construct "quantum" coarse structures and uniform Roe algebras in which the underlying set is replaced with an arbitrary represented von Neumann algebra. The general theory immediately applies to quantum metrics (suitably defined), but it is much richer. We explain another source of examples based on measure instead of metric, leading to a large and easy-to-understand class of new C*-algebras.
I will present the big picture: where uniform Roe algebras come from, how Weaver's framework facilitates our definitions. I will focus on a few illustrative examples and will not assume any familiarity with coarse structures or von Neumann algebras.

E.T.A. Kakariadis (Newcastle, UK)
2022-02-11 15:00 - 16:30 | https://stable.researchseminars.org/talk/AthensFAOA/27/
Title: Rigidity of analytic operator algebras (https://stable.researchseminars.org/talk/AthensFAOA/27/)
by E.T.A. Kakariadis (Newcastle, UK) as part of Functional analysis and operator algebras in Athens

Abstract
Abstract: In the past 20 years, nonselfadjoint algebras have been proven to
provide complete invariants for geometric structures. This follows from a
combination of techniques from Complex Analysis, Functional Analysis and
Algebra. In this talk I will survey on rigidity results for analytic operator
algebras related to subproduct systems and semigroups. In some cases, this is in
stark contrast to what happens with C*-algebras.

E.T.A. Kakariadis (Newcastle, UK)
2022-02-18 15:00 - 16:30 | https://stable.researchseminars.org/talk/AthensFAOA/28/
Title: Rigidity of analytic operator algebras (2nd talk) (https://stable.researchseminars.org/talk/AthensFAOA/28/)
by E.T.A. Kakariadis (Newcastle, UK) as part of Functional analysis and operator algebras in Athens

Abstract
Abstract: In the past 20 years, nonselfadjoint algebras have been proven to
provide complete invariants for geometric structures. This follows from a
combination of techniques from Complex Analysis, Functional Analysis and
Algebra. In this talk I will survey on rigidity results for analytic operator
algebras related to subproduct systems and semigroups. In some cases, this is in
stark contrast to what happens with C*-algebras.

N. Spronk (Waterloo, Canada)
2022-02-25 15:00 - 16:30 | https://stable.researchseminars.org/talk/AthensFAOA/29/
Title: Topologies, idempotents and ideals (https://stable.researchseminars.org/talk/AthensFAOA/29/)
by N. Spronk (Waterloo, Canada) as part of Functional analysis and operator algebras in Athens

Abstract
Let $G$ be a topological group. I wish to exhibit a bijection between (i) a certain class of weakly almost periodic topologies, (ii) idempotents in the weakly almost periodic compactification of $G$, and (iii) certain ideals of the algebra of weakly almost periodic functions. This has applications to decomposing weakly almost periodic representations on Banach spaces, generalizing results which go back to many authors.

Moving to unitary representations, I will develop the Fourier-Stieltjes algebra $B(G)$ of $G$, and give the analogous result there. As an application, I show that for a locally compact connected group, operator amenability of $B(G)$ implies that $G$ is compact, partially resolving a problem of interest for 25 years.

D. Andreou (NKUA)
2022-03-04 15:00 - 16:30 | https://stable.researchseminars.org/talk/AthensFAOA/30/
Title: Crossed products of operator spaces and approximation properties (https://stable.researchseminars.org/talk/AthensFAOA/30/)
by D. Andreou (NKUA) as part of Functional analysis and operator algebras in Athens

Abstract
We will discuss two notions of crossed product for group actions as
well as coactions on dual operator spaces, which generalize the usual von
Neumann algebra crossed product. The goal is to describe certain group
approximation conditions, such as the Haagerup-Kraus approximation property
and Ditkin's condition at infinity, through properties of the associated crossed
product functors.

NO TALK
2022-04-22 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/31/
Title: NO TALK (https://stable.researchseminars.org/talk/AthensFAOA/31/)
by NO TALK as part of Functional analysis and operator algebras in Athens

Abstract: TBA

NO TALK
2022-04-29 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/32/

Stefaan Vaes (KU Leuven)
2022-05-06 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/33/
Title: W$^*$-rigidity paradigms for embeddings of II$_1$ factors (https://stable.researchseminars.org/talk/AthensFAOA/33/)
by Stefaan Vaes (KU Leuven) as part of Functional analysis and operator algebras in Athens

Abstract
I will report on a joint work with Sorin Popa in which we undertake a systematic study on the following question: when can a given II$_1$ factor be embedded into another given II$_1$ factor? More generally, we say that a II$_1$ factor $M$ stably embeds into a II$_1$ factor $N$ if $M$ may be realized as a subfactor of an amplification of $N$, not necessarily of finite index. We provide families of II$_1$ factors that are mutually non stably embeddable, as well as families that are mutually embeddable, yet nonisomorphic. We prove that the preorder relation of stable embeddability is as complicated as it can be since it contains any partially ordered set. We also obtain numerous computations of invariants of II$_1$ factors, including descriptions of all stable self embeddings, outer automorphism groups, etc.

Tr. Russell (U.S.M.A. Westpoint)
2022-04-15 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/34/
Title: An operator system approach to quantum correlations (https://stable.researchseminars.org/talk/AthensFAOA/34/)
by Tr. Russell (U.S.M.A. Westpoint) as part of Functional analysis and operator algebras in Athens

Abstract
In this talk, I will explain a novel approach to Tsirelson's problem
using the theory of operator systems. Tsirelson's problem relates to whether the
commuting operator model of quantum mechanics produces different statistics
than the tensor product model of quantum mechanics in non-local measurement
scenarios. These questions have been shown to be equivalent to Connes'
embedding problem from the theory of Von Neumann algebras. After
tremendous effort by physicists, mathematicians, and computer scientists,
Tsirelson's problem was finally resolved in a recent paper. Nevertheless,
interest in understanding Tsirelson's problem in greater detail remains. After
exploring some background in the theory of operator systems, I will explain
how to characterize quantum correlations using only abstract operator system
theory, building upon existing C*-algebraic and operator theoretic
characterizations in the literature. This new characterization yields an
equivalent restatement of Tsirelson's problem in the language of abstract
operator systems.

G. Pisier (Texas A&M, USA, Sorbonne Universite, Fr.)
2022-03-11 15:00 - 16:30 | https://stable.researchseminars.org/talk/AthensFAOA/35/
Title: The lifting property for C* algebras (https://stable.researchseminars.org/talk/AthensFAOA/35/)
by G. Pisier (Texas A&M, USA, Sorbonne Universite, Fr.) as part of Functional analysis and operator algebras in Athens

Abstract
We give several characterizations of the lifting property (LP in short) using the maximal tensor product for C* -algebras. The class of algebras with LP includes all nuclear C*-algebras but also the full C*-algebras of free groups. The local version of the LP (LLP in short) will be discussed in connection with the problem whether the local LP implies the global LP in the separable case.

O.M. Shalit (Technion, Haifa)
2022-05-13 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/36/
Title: CP-semigroups and dilations, subproduct systems and superproduct systems (https://stable.researchseminars.org/talk/AthensFAOA/36/)
by O.M. Shalit (Technion, Haifa) as part of Functional analysis and operator algebras in Athens

Abstract
In a joint work with Michael Skeide, we introduce a framework for studying dilations of semigroups of completely positive maps on C*-algebras. The heart of our method is the systematic use of families of Hilbert C*-correspondences that behave nicely with respect to tensor products: these are product systems, subproduct systems and superproduct systems. Although we developed our tools with the goal of understanding the multi-parameter case, they also lead to new results even in the well studied one parameter case. In my talk I will give a broad outline of our work.

D. Pitts (University of Nebraska-Lincoln)
2022-04-08 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/37/
Title: Normalizers and Approximate Units for Inclusions of C*-Algebras (https://stable.researchseminars.org/talk/AthensFAOA/37/)
by D. Pitts (University of Nebraska-Lincoln) as part of Functional analysis and operator algebras in Athens

Abstract
Consider {\it inclusions}, which are pairs of $C^*$-algebras $(C,D)$ with $D$ an abelian subalgebra of $C$. An element $v\in C$ {\it normalizes} $D$ if $v^*D v \cup vDv^* \subseteq D$. The inclusion $(C,D)$ is {\it regular} when the linear span of the normalizers is dense in $C$ and is {\it singular} when every normalizer belongs to $D$.

I will prove a commutation result for Hermitian normalizers, then discuss some consequences of this result related to familiar constructions. Sample consequence:
when $D$ is a regular MASA in $C$, every approximate unit for $D$ is an approximate unit for $C$; this leads to simplifiation of the notions of Cartan MASA and $C^*$-diagonal in the non-unital setting.

The inclusion $(C,D)$ is {\it intermediate} to the regular MASA inclusion $(B,D)$ if $D\subseteq C\subseteq B$.
I will give examples showing some singular MASA inclusions are intermediate to regular MASA inclusions, but others are not, and will discuss the fact that when $\mathcal H$ is a separable, infinite dimensional Hilbert space, no MASA inclusion of the form $(\mathcal B(\mathcal H), D)$ is intermediate to a regular MASA inclusion.

E. Gillaspy (U. Montana, USA)
2022-05-27 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/38/
Title: Cartan subalgebras in groupoid C*-algebras (https://stable.researchseminars.org/talk/AthensFAOA/38/)
by E. Gillaspy (U. Montana, USA) as part of Functional analysis and operator algebras in Athens

Abstract
Building on earlier work of Kumjian, Renault proved in 2008 that a C*-algebra $A$ has a Cartan subalgebra $B$ if and only if there is a topologically principal groupoid $W$ whose twisted C*-algebra $C^*(W; S)$ is isomorphic to $A$. In fact, $W$ (the Weyl groupoid of the Cartan pair $(B, A)$) can be constructed from $A$ and $B$. However, a groupoid $W$ does not have to be topologically principal in order to construct $C^*(W; S)$. Do those more general groupoid C*-algebras have Cartan subalgebras, and if so, what is the relationship between the Weyl groupoid and the original groupoid?

In joint work with A. Duwenig, R. Norton, S. Reznikoff, and S. Wright, we identified situations when a subgroupoid $S$ of a non-principal groupoid $G$ will give rise to a Cartan subalgebra $B = C^*(S)$ of $A = C^*(G)$. Subsequent work, joint with A. Duwenig and R. Norton, revealed that in this case, the Weyl groupoid $W$ of the pair $(B, A)$ is a semidirect product: $W = G/S \ltimes \widehat{S}$. We also describe the Weyl twist explicitly in the situation where there is a continuous section $G/S \to G$. Furthermore, ongoing joint work with J.H. Brown has established that the description of the Weyl groupoid is valid even in the more general setting of $\Gamma$-Cartan pairs.

If you're still mostly lost after reading this abstract, never fear! The talk will not assume familiarity with groupoids, their C*-algebras, or Cartan subalgebras for C*-algebras, and should (I hope) be more comprehensible.

M. Brannan (U. Waterloo, Canada)
2022-05-20 13:00 - 14:30 | https://stable.researchseminars.org/talk/AthensFAOA/39/
Title: Quantum path spaces, correspondences, and quantum Cuntz-Krieger algebras NOTE UNUSUAL TIME (https://stable.researchseminars.org/talk/AthensFAOA/39/)
by M. Brannan (U. Waterloo, Canada) as part of Functional analysis and operator algebras in Athens

Abstract
In recent years there has been a significant interest in studying generalizations of graphs within the framework of noncommutative geometry. Such objects are called quantum graphs. In this talk I will explain what a quantum graph is, and also introduce quantum Cuntz-Krieger (QCK) algebras, which are a class of universal C*-algebras associated to quantum graphs previously introduced by Eifler, Voigt, Weber and the speaker.
As the name suggests, QCK algebras generalize Cuntz-Krieger algebras of ordinary graphs, but they turn out to be very hard to understand. In this talk I will explain some attempts to better understand QCK algebras by considering quantum analogues of graph correspondences and their associated Cuntz-Pimsner algebras, as well as infinite quantum path spaces and their associated Exel crossed products.
This is based on joint work with Mitch Hamidi, Lara Ismert, Brent Nelson and Mateusz Wasilewski.

NOTE UNUSUAL TIME

M. Ghandehari (U. Delaware)
2022-03-18 15:00 - 16:30 | https://stable.researchseminars.org/talk/AthensFAOA/40/
Title: Meaningful decay behavior of higher dimensional continuous wavelet transforms (https://stable.researchseminars.org/talk/AthensFAOA/40/)
by M. Ghandehari (U. Delaware) as part of Functional analysis and operator algebras in Athens

Abstract
The wavefront set of a tempered distribution $u$ is the set of points $t\in{\mathbb R}^n$ and directions $\xi$ in the sphere $S^{n-1}$ along which $u$ is not smooth at $t$. In the recent years, certain wavelet-type transformations (for example the curvelet or shearlet transformation) have gained considerable attention, due to their potential for identifying the wavefront set of a signal by inspecting the decay rate of the corresponding transformation coefficients.

Recently, many efforts have been made aiming to generalize the above characterization for higher dimensional cases. Higher dimensional wavelet transforms are constructed using square-integrable representations of ${\mathbb R}^n\rtimes H$ where $H$ can be any suitably chosen dilation group. In this talk, we consider the problem of characterizing the Sobolev wavefront set of a distribution for a higher-dimensional wavelet transform in two important cases where: 1) the mother wavelet is compactly supported, and 2) the mother wavelet has compactly supported Fourier transform.

This talk is based on an ongoing joint project with Hartmut Fuhr.

NO TALK
2022-03-25 15:00 - 16:30 | https://stable.researchseminars.org/talk/AthensFAOA/41/

A. Ioana (UCSD, USA)
2022-04-01 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/42/
Title: Wreath-like product groups and rigidity of their von Neumann algebras (https://stable.researchseminars.org/talk/AthensFAOA/42/)
by A. Ioana (UCSD, USA) as part of Functional analysis and operator algebras in Athens

Abstract
In this talk, I will introduce a new class of groups, called wreath-like products. These groups are close relatives of the classical wreath products and arise naturally in the context of group theoretic Dehn filling. Unlike ordinary wreath products, many wreath-like products have Kazhdan's property (T). I will present several new rigidity results for von Neumann algebras of wreath-like products with property (T). In particular, we obtain the first examples of property (T) groups $G$ which are W*-superrigid, in the sense that the group von Neumann algebra $\text{L}(G)$ remembers the isomorphism class of $G$. We also compute the automorphism and fundamental groups of von Neumann algebras of a wide class of wreath-like products. As an application, we show every finitely presented group can be realised as the outer automorprhism group of $\text{L}(G)$ for a property (T) group $G$. This is based on joint work with Ionut Chifan, Denis Osin and Bin Sun.

Y. Choi (U. Lancaster, UK)
2022-06-03 14:00 - 15:30 | https://stable.researchseminars.org/talk/AthensFAOA/43/
Title: Extensions, unitarizability, and amenable operator algebras (https://stable.researchseminars.org/talk/AthensFAOA/43/)
by Y. Choi (U. Lancaster, UK) as part of Functional analysis and operator algebras in Athens

Abstract
In work with Farah and Ozawa, we exhibited a closed subalgebra of
$\ell^\infty\otimes {\mathbb M}_2$ which is amenable, yet is not
Banach-algebra-isomorphic to any $C^\ast$-algebra; the non-isomorphism
is witnessed by the failure to be "unitarizable" of certain bounded
subgroups of matrix corona algebras. It remains an open question
whether similar "counterexamples" can be found inside $C(K)\otimes
{\mathbb M}_d$ for metrizable $K$. In this talk we report on some work
in progress, joint with B. Green (Lancaster), investigating what can
be said when $K$ has finite Cantor-Bendixson rank.

E. Kakariadis (Newcastle, UK)
2023-01-13 13:00 - 15:00 | https://stable.researchseminars.org/talk/AthensFAOA/44/
Title: Morita equivalence for operator systems I (https://stable.researchseminars.org/talk/AthensFAOA/44/)
by E. Kakariadis (Newcastle, UK) as part of Functional analysis and operator algebras in Athens

Abstract
In ring theory, Morita equivalence preserves many properties of the objects, and generalizes the isomorphism equivalence between commutative rings. A strong Morita equivalence for selfadjoint operator algebras was introduced by Rieffel in the 60s, and works as a correspondence between their representations. In the past 30 years there has been an interest to develop a similar theory for nonselfadjoint operator algebras and operator spaces with much success and in this talk we will review the main points of these works. Then, taking motivation from recent work of Connes and van Suijlekom, we will present a Morita theory for operator systems. We will give equivalent characterizations of Morita equivalence via Morita contexts, bihomomoprhisms and stable isomorphism, while we will highlight properties that are preserved in this context. Finally we will provide applications to rigid systems, function systems and non-commutative graphs.

This is joint work with George Eleftherakis and Ivan Todorov.

E. Kakariadis (Newcastle, UK)
2023-02-03 15:00 - 17:00 | https://stable.researchseminars.org/talk/AthensFAOA/45/
Title: Morita equivalence for operator systems II (https://stable.researchseminars.org/talk/AthensFAOA/45/)
by E. Kakariadis (Newcastle, UK) as part of Functional analysis and operator algebras in Athens

Abstract: TBA

M. Lupini (Bologna, It)
2023-02-10 15:00 - 17:00 | https://stable.researchseminars.org/talk/AthensFAOA/46/
Title: Definable refinements of classical algebraic invariants (https://stable.researchseminars.org/talk/AthensFAOA/46/)
by M. Lupini (Bologna, It) as part of Functional analysis and operator algebras in Athens

Abstract
In this talk I will explain how methods from logic allow one to construct refinements of classical algebraic invariants that are endowed with additional topological and descriptive set-theoretic information. This approach brings to fruition initial insights due to Eilenberg, Mac Lane, and Moore (among others) with the additional ingredient of recent advanced tools from logic. I will then present applications of this viewpoint to invariants from a number of areas in mathematics, including operator algebras, algebraic topology, and homological algebra.

S. Raum (Stockholm, Sw)
2023-02-17 15:00 - 17:00 | https://stable.researchseminars.org/talk/AthensFAOA/47/
Title: Detecting ideals in reduced crossed product C*-algebras of topological dynamical systems (https://stable.researchseminars.org/talk/AthensFAOA/47/)
by S. Raum (Stockholm, Sw) as part of Functional analysis and operator algebras in Athens

Abstract
Crossed products arising from topological dynamical systems are an important source of examples of C*-algebras and form ground for interaction between dynamics and operator algebras. Included in this class are reduced group C*-algebras which code representation theoretic information of a group. Sophisticated tools to prove (non-)simplicity of such C*-algebras have been developed over the time. However, they only apply to well-behaved dynamical systems or exclude a certain kind of amenable behaviour of the dynamical system. I will make these statements precise and report on joint work with Are Austad (University of Southern Denmark) in which we introduce the ℓ¹-ideal intersection property. All non-zero ideals in the crossed product C*-algebra of a dynamical system satisfying this property can be detected already inside the much smaller and more concrete ℓ¹-crossed product. We prove that large classes of groups, such as lattices in Lie groups and linear groups over algebraic integers in a number field have this property for ANY action on a locally compact Hausdorff space. The proof combines the theory of twisted groupoid C*-algebras and C*-simplicity with structure results about amenable subgroups.

G. Hoefer (Delaware, USA)
2023-02-24 15:00 - 17:00 | https://stable.researchseminars.org/talk/AthensFAOA/48/
Title: Quantum hypergraph homomorphisms and applications to non-local games (https://stable.researchseminars.org/talk/AthensFAOA/48/)
by G. Hoefer (Delaware, USA) as part of Functional analysis and operator algebras in Athens

Abstract
Utilizing the simulation paradigm in information theory,
we introduce notions of quantum hypergraph homomorphisms and
quantum hypergraph isomorphisms
by considering different no-signalling correlation classes and the hypergraphs the associated information
channels induce. We provide examples of separation between
classical and quantum hypergraph isomorphism.

For a given hypergraph isomorphism game, we show that the existence of perfect no-signalling (resp. quantum commuting, quantum approximate) strategies can be
characterized in terms of states on tensor products of canonical operator systems.
We further focus on a sub-class of hypergraph homomorphism games where the hypergraphs are themselves non-local games. We define strongly no-signalling correlations and their various subtypes, and investigate game strategy transport and the existence of perfect strategies for games using an operator system approach.

The talk will be based on a joint work with Ivan G. Todorov.

V. Paulsen (Waterloo, Ca)
2023-03-10 15:00 - 17:00 | https://stable.researchseminars.org/talk/AthensFAOA/49/
Title: Matrix range characterizations of operator system properties (https://stable.researchseminars.org/talk/AthensFAOA/49/)
by V. Paulsen (Waterloo, Ca) as part of Functional analysis and operator algebras in Athens

Abstract
Given an operator system S, one can create two sequences of new operator systems from it, denoted $OMAX_k(S)$ and $OMIN_k(S)$. The first is the universal operator system with the property that every k-positive map with domain S is completely positive as a map from $OMAX_k(S)$. The second has the property that every k-positive map with range S is completely positive as a map into $OMIN_k(S)$. A natural question is if these new operator systems in some sense ​``converge to S" as k tends to infinity. The answer is ​``not always", but convergence does characterize certain important properties of S. Finally, when S is the finite dimensional operator system spanned by an N-tuple of operators T=(T_1,...,T_n), then these convergences can be characterized in terms of geometrical properties of the joint matricial ranges of T. Of special importance is the case when (T_1,...,T_n) are the unitary generators of the universal C*-algebra of the free group on n-generators.

I. Beltita (Inst. Math. Romanian Acad.)
2023-03-17 15:00 - 17:00 | https://stable.researchseminars.org/talk/AthensFAOA/50/
Title: $C^*$-rigidity for certain exponential Lie groups (https://stable.researchseminars.org/talk/AthensFAOA/50/)
by I. Beltita (Inst. Math. Romanian Acad.) as part of Functional analysis and operator algebras in Athens

Abstract
A exponential Lie group is called (stably) $C^*$-rigid if it is uniquely determined, within the class of exponential Lie groups, by the class of isomorphism (Morita equivalence) of its $C^*$ algebra. We discuss the problem of $C^*$-rigidity of exponential Lie groups. In particular, we show that generalized $ax+b$-groups are non-rigid, while nilpotent Lie groups of dimension less than equal to 5 are stably $C^*$-rigid.

Matthew Daws (University of Central Lancashire, UK)
2023-03-03 15:00 - 17:00 | https://stable.researchseminars.org/talk/AthensFAOA/51/
Title: Around the Approximation Property for Quantum Groups (https://stable.researchseminars.org/talk/AthensFAOA/51/)
by Matthew Daws (University of Central Lancashire, UK) as part of Functional analysis and operator algebras in Athens

Abstract
I will introduce what the "approximation property" (AP) is for (locally compact) groups, and provide a few applications. I will then talk about how one might give an analogous definition for (locally compact) quantum groups, explaining some of the needed technology along the way.

Pavlos Motakis (York University)
2023-03-24 15:00 - 17:00 | https://stable.researchseminars.org/talk/AthensFAOA/52/
Title: Separable spaces of continuous functions as Calkin algebras (https://stable.researchseminars.org/talk/AthensFAOA/52/)
by Pavlos Motakis (York University) as part of Functional analysis and operator algebras in Athens

Abstract
For a Banach space $X$ denote $\mathcal{L}(X) = \{T:X\to X\text{ linear and bounded}\}$ and $\mathcal{K}(X) = \{T\in\mathcal{L}(X): T\text{ compact}\}$. The Calkin algebra of $X$ is the Banach algebra $\mathcal{C}al(X) = \mathcal{L}(X)/\mathcal{K}(X)$. A question that has gathered attention in recent years is what unital Banach algebras admit representations as Calkin algebras. We discuss developments in this topic as well as a recent contribution, namely that for every compact metric space $K$ there exists a Banach space $X$ so that $\mathcal{C}al(X)$ coincides isometrically with $C(K)$ as a Banach algebra.

Alexandros Eskenazis (Sorbonne, Fr & Cambridge, UK)
2023-04-07 14:00 - 16:00 | https://stable.researchseminars.org/talk/AthensFAOA/53/
Title: Discrete logarithmic Sobolev inequalities in Banach spaces (https://stable.researchseminars.org/talk/AthensFAOA/53/)
by Alexandros Eskenazis (Sorbonne, Fr & Cambridge, UK) as part of Functional analysis and operator algebras in Athens

Abstract
We shall discuss certain aspects of vector-valued harmonic analysis on the discrete hypercube. After presenting the geometric motivation behind such investigations, we will survey known results on the Poincaré inequality and Talagrand’s influence inequality. Then we will proceed to present a new optimal vector-valued logarithmic Sobolev inequality in this context. The talk is based on joint work with D. Cordero-Erausquin (Sorbonne).

Petros Valettas (U. Missouri, USA)
2023-05-19 14:00 - 16:00 | https://stable.researchseminars.org/talk/AthensFAOA/56/
Title: Probabilistic Padé Problems (https://stable.researchseminars.org/talk/AthensFAOA/56/)
by Petros Valettas (U. Missouri, USA) as part of Functional analysis and operator algebras in Athens

Abstract
It has been observed, by Froissart (1969), that zeros and poles of higher order Padé approximants of random perturbations of a deterministic Taylor series tend to form unstable pairs. These pairs appear at loci characteristic of the random part in the coefficients of the Taylor series. While this phenomenon has only been confirmed experimentally, it has been suggested, and indeed used, as a noise detection tool. In this talk we will explain how techniques from high-dimensional probability and logarithmic potential theory can be melted together to rigorously establish and quantify the clustering of zeros in the ``pure noise’’ case, when the coefficients are drawn according to a distribution with anti-concentration properties.

Based on a joint ongoing work with S. Dostoglou (University of Missouri).

E.T.A. Kakariadis (Newcastle U., UK)
2023-03-31 12:00 - 14:00 | https://stable.researchseminars.org/talk/AthensFAOA/57/
Title: Entropy and phase transitions for KMS-states of Pimsner-type algebras (https://stable.researchseminars.org/talk/AthensFAOA/57/)
by E.T.A. Kakariadis (Newcastle U., UK) as part of Functional analysis and operator algebras in Athens

Abstract
There is a well-developed theory of Kubo-Martin-Schwinger states (or equilibrium states) for C*-algebras, which are motivated by the properties of Gibbs states for finite matrices. They have attracted interest as they provide an invariant for classification up to equivariant isomorphisms of C*-algebras. There has been a growing study of their parametrization in particular for C*-algebras coming from Hilbert modules, which are generalizations of the Toeplitz and Cuntz algebras. In this talk I will give an overview about the theory of KMS states in this setting and present how the notion of entropy allows to identify phase transitions. Time permitting we will discuss how this works for graph algebras and Nica-Pimsner algebras.

Sarah Reznikoff (Kansas State U., USA)
2023-04-28 14:00 - 16:00 | https://stable.researchseminars.org/talk/AthensFAOA/58/
Title: Notes on regular ideals of C*-algebras (https://stable.researchseminars.org/talk/AthensFAOA/58/)
by Sarah Reznikoff (Kansas State U., USA) as part of Functional analysis and operator algebras in Athens

Abstract
We define and discuss the regular ideals of $C^*$-algebras including the special case of graph algebras, in particular properties preserved by quotients of regular ideals. This is joint work with Jonathan Brown, Adam Fuller, and David Pitts.

Ebrahim Samei (U. Saskatchewan, Canada)
2023-05-05 14:00 - 16:00 | https://stable.researchseminars.org/talk/AthensFAOA/59/
Title: New tensor products of C*-algebras and characterization of type I C*-algebras as rigidly symmetric C*-algebras (https://stable.researchseminars.org/talk/AthensFAOA/59/)
by Ebrahim Samei (U. Saskatchewan, Canada) as part of Functional analysis and operator algebras in Athens

Abstract
C*-algebras are studied through various tools and techniques including their tensor products. There are several classes of tensor products that have been considered and studied extensively on C*-algebras. We introduce a new class of such objects using the theory of complex interpolations on operator spaces. Our construction allows us to produce a continuum family of distinct tensor product of the reduced C*-algebras of nonamenable groups possessing both the rapid decay and Haagerup property. We will show that they are in fact in the form of a Brown-Guentner type C*-completion. As another application of our approach, we provide a complete answer to a question of Leptin and Poguntke from 1979 proving that a C*-algebra is rigidly symmetric if and only if it is type I.

This talk is based on a joint work with Hun Hee Lee (SNU) and Matthew Wiersma (U of Winnipeg).

S. Petrakos (WWU Münster, Germany)
2023-05-12 14:00 - 16:00 | https://stable.researchseminars.org/talk/AthensFAOA/60/
Title: Dynamical Alternating Groups (https://stable.researchseminars.org/talk/AthensFAOA/60/)
by S. Petrakos (WWU Münster, Germany) as part of Functional analysis and operator algebras in Athens

Abstract
Topological full groups form a very important class of groups arising from
dynamical systems and, more generally, étale groupoids. Their subgroups, especially the
alternating subgroup, have been proven to exhibit various properties, some of which were
rarely or never before witnessed. In this talk I will introduce these groups in the dynamical
setting and go through some of the most important past results on the topic, focusing on
those of operator-algebraic interest. I will then briefly introduce the concept of almost
finiteness and present a recent result obtained in joint work with Petr Naryshkin. We prove
that if a subgroup of a TFG is amenable and contains the alternating subgroup, then all its
free actions on finite-dimensional compact metrizable spaces are almost finite.

G. Kopsacheilis (WWU Münster. Germany)
2023-05-26 14:00 - 16:00 | https://stable.researchseminars.org/talk/AthensFAOA/61/
Title: A comparison type property for Cartan subalgebras (https://stable.researchseminars.org/talk/AthensFAOA/61/)
by G. Kopsacheilis (WWU Münster. Germany) as part of Functional analysis and operator algebras in Athens

Abstract
Regularity properties of C*-algebras are vital for classification theory. In the C*-setting, finite nuclear dimension, tensorial absorption of the Jiang--Su algebra and strict comparison set the stage for Elliott's classification programme; these properties are known to be tightly related, as the (to a large extent confirmed) Toms--Winter conjecture predicts. On the dynamical side, analogues of these have been introduced for group actions, and it is not yet quite clear how these relate to the regularity properties of the crossed product. In this talk, we introduce a comparison type property in the context of Cartan subalgebras and study its relations to regularity properties of the ambient C*-algebra, and of the underlying dynamics, when the inclusion arises from a topological dynamical system.
This talk is based on joint work (in progress) with Wilhelm Winter.
