David Blecher (Houston)
'Interpolating' between Hilbert space operators, and real positivity
for operator algebras
With Charles Read we have introduced and studied a new notion of (real)
positivity in operator algebras, with an eye to extending certain $C^*$-algebraic
results and theories to more general algebras. As motivation note that the
`completely' real positive maps on C*-algebras or operator systems are precisely
the completely positive maps in the usual sense; however with real positivity
one may develop a useful order theory for more general spaces and algebras.
This is intimately connected to new relationships between an operator algebra
and the C*-algebra it generates, and in particular what to we call noncommutative
peak interpolation, and noncommutative peak sets. We report on the state
of this theory (joint work with Read, ome in progress at the time of writing)
and on the parts of it that generalize further to certain classes of Banach
algebras (joint work with N. Ozawa).
Ken Davidson (Waterloo)
Semicrossed products over semigroups
If $P$ is a subsemigroup of a group $G$ that acts on a C*-algebra $A$ by
$*$-endomorphisms, we construct the semicrossed product, which is a universal
nonself-adjoint operator algebra with respect to some specified family of
covariant representations. We seek to identify the C*-envelope, which is
the smallest enveloping C*-algebra, as a crossed product of a related C*-algebra
$B$ by an automorphic action of $G$. This is accomplished in a number of
cases.
This is joint work with Adam Fuller (U. Nebraska) and Evgenios Kakariadis
(Ben-Gurion U.).
Ilijas Farah (York)
A new tool for constructing nuclear C*-algebras
By combining old and new tools from model theory one can give unified proofs
of various permanence properties for C*-algebras defined by approximation
properties. These tools also provide new constructions of C*-algebras with
prescribed properties. This is a report on work in progress with several
coauthors, including B. Hart, M. Magidor, L. Robert and A. Tikuisis.
Farzad Fathizadeh (Caltech and Western )
Scalar Curvature and Gauss-Bonnet Theorem for Noncommutative Tori
Coauthors; Masoud Khalkhali
After the seminal work of Connes and Tretkoff on the Gauss-Bonnet theorem
for the noncommutative two-torus, there have been significant developments
in understanding the local differential geometry of these C*-algebras equipped
with curved metrics. In this talk, I will review my joint works with M.
Khalkhali in which we extend this result to general translation invariant
conformal structures on noncommutative two-tori and compute the scalar curvature.
Our final formula for the curvature matches precisely with the one computed
independently by A. Connes and H. Moscovici. A purely noncommutative feature
in these works is the appearance of the modular automorphism from Tomita-Takesaki
theory in the computations and final formulas for the curvature. Time permitting
I shall also try to indicate an extension of these results to curved noncommutative
four tori.
Fereidoun Ghahramani (Manitoba)
An introduction to approximate amenability for operator algebraists
This talk is on basic material from theory of {\it approximate
amenability} and its branches that R.J. Loy and I introduced in the year 2000
and have been developing since then, sometimes with other colleagues: Y. Choi,
H.G. Dales, C.J. Read, E. Samei, and Y. Zhang. I have chosen the material
for the talk so that it might be interesting for operator algebraists. Although
some results to be presented are about operator algebras on Banach spaces,
the talk, however, will end up with some open questions on operator algebras
on Hilbert spaces.
Thierry Giordano (Ottawa)
Purely infinite partial crossed products
Partial actions of a discrete group on C*-algebras and their associated
crossed products were introduced by Ruy Exel and Kevin McClanahan, and since
then have been developed by many authors. In a recent work, Adam Sierakowski
and I pursued the study of partial C*-dynamical systems and their associated
crossed products. In this talk I will report on some of the results we obtained.
Guihua Gong (Puerto Rico)
TBA
Matthew Kennedy (Carleton)
Boundaries of reduced C*-algebras of discrete groups
For a discrete group G, we consider the minimal C*-algebra of $\ell^\infty(G)$
that arises as the image of a unital positive G-equivariant projection.
This algebra always exists and is unique up to isomorphism. It is trivial
if and only if G is amenable. We prove that, more generally, it can be identified
with the C*-algebra of continuous functions on Furstenberg’s universal
G-boundary. This operator-algebraic construction of the Furstenberg boundary
turns out to have some interesting consequences. In particular, it leads
to proof of a conjecture of Ozawa about nuclear embeddings of reduced C*-algebras
of exact groups.
Masoud Khalkhali (Western)
Spectral Geometry of Curved Noncommutative Tori
While the algebraic topology of noncommutative tori, as reflected in their
K-theory, cyclic cohomology and index theory, have been intensively studied
in the past three decades, much less is known about their geometry.
Ideas of spectral geometry, even the very notion of Riemannian metric itself,
can often be imported to noncommutative geometry thanks to Connes' notion
of spectral triples. This gives an opening to geometric studies of noncommutative
spaces endowed with a suitable notion of curved metric. In this talk I shall
survey recent joint work with Farzad Fathizadeh, and the closely related
work of Connes-Tretkoff and Connes-Moscovici, on Gauss-Bonnet theorem and
the scalar curvature for curved
noncommutative tori $A_{\theta}^n $ for $ n=2, 4.$ In dimension 2 the local
expression for curvature, as an element of the noncommutative torus, is
computed by evaluating the value of the (analytic continuation of the) spectral
zeta function $\zeta_a(s) = \text{Trace} (a |D|^{-s})$ at $s=0$ as a linear
functional in $ a\in C^{\infty}({T}_{\theta}^2)$. In higher dimensions scalar
curvature is related to the residue of the spectral zeta functions at its
subleading pole.
Eberhard Kirchberg (HU Berlin)
`Central sequence algebras with and without characters
The ``corrected'' central sequence algebra F(A) of a separable C*-algebra
A contains basic information about properties of A. An important question
is: When F(A) is character-less? We report on two different aspects of this
questions that we study in papers with Mikael Rordam and with Hiroshi Ando.
E.g. we show that F(A) contains a unital C*-subalgebra that has B(H) as
a unital quotient if A is anti-liminal. We give examples where F(A) has
a character.
If F(A) has no character then A has the strong corona factorization property
of Kucerovsky and Ng.
Additional assumptions on $A$ , like a rather strong 2-splitting property
or divisibility and comparability properties, allow to show that
F(A) contains the the Jiang-Su algebra Z unitally as subalgebra (i.e., A
absorbs Z tensorial) if F(A) has no character.
James Mingo (Queen’s)
Freeness and the Transpose
Over twenty years ago Voiculescu showed that independent and unitarily
invariant random matrices are asymptotically free. Asymptotic freeness gives
universal rules for computing (asymptotically) the eigenvalue distribution
of sums and products of random matrices provided that one knows the individual
eigenvalue distribution.
The requirement that the ensembles be unitarily invariant was lifted recently
but the requirement that the ensembles be independent has always been necessary
until a year ago when Mihai Popa and I showed that a matrix can be asymptotically
free from its transpose. Recently we have show that this can pushed to the
partial transposes of interest in quantum information theory.
Magdalena Musat (Copenhagen)
Factorizable completely positive maps and the Connes embedding problem
Zhuang Niu (Wyoming)
The C*-algebra of a minimal homeomorphism with zero mean dimension
Consider a minimal homeomorphism of a compact metrizable space, and assume
that it has zero mean topological dimension (a dynamical version of topological
covering dimension which was introduced by Lindenstrauss and Weiss). It
is shown that the crossed product C*-algebra absorbs Jiang-Su algebra tensorially.
This is a joint work with George A. Elliott.
N. Christopher Phillips (Oregon)
Examples of operator algebras on L^p spaces: Simplicity, uniqueness
theorems, and amenability
We describe several classes of operator algebras on L^p spaces which, despite
not having an adjoint, share some good properties of C*-algebras, and about
which enough can be said to suggest that there may be a rich theory of such
algebras. Our examples include:
L^p analogs of UHF and AF algebras.
L^p analogs of Cuntz algebras.
Full and reduced group L^p operator algebras.
L^p operator crossed products, particularly by free minimal actions
on compact metric spaces.
The L^p analog of the C*-algebra of the unilateral shift.
We consider simplicity, uniqueness results (analogous to those for the
Cuntz C*-algebras), pure infiniteness, K-theory, amenability, p-nuclearity,
and the relations between the structure of a group and L^p operator algebras
built using it. A great many open problems remain. (There is a pdf file
of some of them on the website of the 2014 GPOTS [Great Plains Operator
Theory Seminar], at
http://www.math.ksu.edu/events/conference/gpots2014/LpOpAlgQuestions.pdf.)
This talk is related to my recent talk at GPOTS, but differs substantially.
It has a different emphasis, and some of what I said in the earlier talk
is already out of date. (There is a TeX version of my GPOTS talk on the
conference website, at
http://www.math.ksu.edu/events/conference/gpots2014/Phillips_loaq.)
Mikael Pichot (McGill)
TBA
Ian Putnam (Victoria)
Smale spaces, their C*-algebras and a homology theory for them.
I will describe some hyperbolic topological dynamical systems called Smale
spaces which were introduced by David Ruelle, giving a number of different
examples including shifts of finite type. I will discuss the construction
of various C*-algebras from these systems; in the case of shifts of finite
type these include the Cuntz-Krieger algebras and their AF cores. I will
also describe a homology theory for Smale spaces, why one might have been
looking for such a theory and how the C*-algebras provide a key ingredient
in the definition.
Mikael Rørdam (Copenhagen)
Elementary amenable groups have quasidiagonal C*-algebra
Rosenberg proved in 1987 that if the C*-algebra of a discrete group is
quasidiagonal, then the group is amenable, and he conjectured that the converse
also holds. Using techniques from the classification of C*-algebras and
a description of elementary amenable groups due to Chou and Osin we confirm
Rosenberg's conjecture for elementary amenable groups. We also show that
these group C*-algebras are AF-embeddable. Our methods extend to show that
also group C*-algebras of amenable LEF groups are AF-embeddable.
This is a joint work with N. Ozawa and Y. Sato.
Zhong-Jin Ruan (Illinois)
Exotic (Quantum) Group C*-algebras
Volker Runde (Alberta)
Dual Banach algebras - an overview
A dual Banach algebra is a Banach algebra that is also a dual Banach space
such that multiplication is separately weak* continuous. Von Neumann algebras
are dual Banach algebras, but so are the measure algebras of locally compact
groups. We discuss amenability properties for dual Banach algebras as well
as their surprisingly intricate representation theory.
Luis Santiago (Aberdeen)
TBA
Aaron Tikuisis (Aberdeen)
The dimension of approximately subhomogeneous C*-algebras
Coauthors : George Elliott, Luis Santiago, Wilhelm Winter
Viewed as a noncommutative topological space, it is quite sensible to try
to define the dimension of a C*-algebra, and many fruitful concepts have
arisen from doing so. I will focus on decomposition rank and ASH dimension,
two dimension-like invariants which are important to the classification
of C*-algebras. It is conjectured that for simple ASH algebras, the decomposition
rank and the ASH dimension always agree and lie in the range $\{0,1,2,\infty\}$.
This conjecture is closely related to the Toms-Winter conjecture and a revived
Elliott conjecture. It is moreover corroborated by various results, some
but not all of which use classification. I will discuss some new developments
related to this conjecture.
Andrew Toms (Purdue)
Mean Dimension and crossed products
Wilhelm Winter (Münster)
Regularity of nuclear C*-algebras
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