Organizer: Dietmar Bisch

Mondays, 4:10-5:30pm in SC 1310

• Date: 8/28/06
  • Speaker: Dietmar Bisch, Vanderbilt University
  • Title: Introduction to II₁ factors and subfactors
  • Abstract: I will give an introduction to von Neumann
    algebras and the theory of subfactors. This meeting serves also
    as organizational meeting for the Subfactor Seminar.
• Date: 9/4/06
  • Speaker: Shamindra Ghosh, Vanderbilt University
  • Title: Introduction to planar algebras I
  • Abstract: We define planar algebras, give some
    examples and explain how they are related to subfactors.
• Date: 9/11/06
  • Speaker: Pinhas Grossman, Vanderbilt University
  • Title: Introduction to planar algebras II
  • Abstract: We continue the introduction to Jones’ planar
    algebra formalism from last week. We will present several
    examples of planar algebras.
• Date: 9/18/06
  • Speaker: Remus Nicoara, Vanderbilt University
  • Title: Group von Neumann algebras, crossed products
    and property T
  • Abstract: This lecture will be an introductory lecture covering
    some of the background material needed for Stefaan Vaes’ lecture series.

• Date: 9/22/06 (Friday), Special Subfactor Seminar,
  Lecture Series by Stefaan Vaes, Lecture I at 3:10pm in SC 1310
  • Speaker: Stefaan Vaes, Katholieke Universiteit Leuven and CNRS Paris
  • Title: Deformation and rigidity results for crossed product
    II₁ factors I
  • Abstract:
    I will present an introduction to recent work of Popa on Bernoulli
    actions of property (T) groups. The main goal is to present the proof of
    Popa’s strong rigidity theorem: the II₁ factors given by the
    Bernoulli action of an ICC property (T) group essentially remember the
    group and the action.

    Lecture 1. I will explain how unitary conjugacy of subalgebras
    of a II₁ factor can be shown using bimodules.
    
    Lecture 2. A strong deformation property of Bernoulli actions, called
    malleability, is played against property (T) to approach the strong
    rigidity theorem.
    
    Lecture 3. The strong rigidity theorem is shown. I will also discuss
    how the techniques of the first two lectures are used in my recent
    joint work with Popa, yielding a lot of explicit computations of outer
    automorphism groups of II₁ factors.

• Date: 9/25/06
  • Speaker: Stefaan Vaes, Katholieke Universiteit Leuven and CNRS Paris
  • Title: Deformation and rigidity results for crossed product
    II₁ factors II

• Date: 9/26/06 (Tuesday), Special Subfactor
  Seminar, 4:10pm in SC 1432
  • Speaker: Stefaan Vaes, Katholieke Universiteit Leuven and CNRS Paris
  • Title: Deformation and rigidity results for crossed product
    II₁ factors III

• Date: 9/27/06 (Wednesday), Topology & Group Theory
  Seminar, Lecture Series by Andreas Thom, Lecture I at 4:10pm in SC 1310
  
  • Speaker: Andreas Thom, University of Goettingen
  • Title: L²-invariants for groups and von Neumann algebras
  • Abstract:
    In recent work, Connes and Shlyakhtenko have defined
    L²-invariants for tracial algebras, generalizing
    L²-invariants for groups
    due to Atiyah-cheeger-Gromov. The study of these L²-invariants
    combines nicely analytic and homological methods. In this talk, we will
    introduce the subject and give an account of the known results and
    open questions that area.

• Date: 9/28/06 (Thursday), RTG Seminar,
  1:10pm in SC 1310
  • Speaker: Andreas Thom, University of Goettingen
  • Title: L²-invariants for groups and von Neumann
    algebras II

• Date: 10/3/06 (Tuesday), NCG Seminar,
  4:10pm in SC 1432
  • Speaker: Andreas Thom, University of Goettingen
  • Title: L²-invariants for groups and von Neumann algebras IV
• Date: 10/9/06
  • Speaker: Jesse Peterson, UC Berkeley
  • Title: Deformation/Rigidity Techniques in von Neumann Algebras
  • Abstract:
    I will discuss the deformation/rigidity techniques introduced
    by Sorin Popa. These techniques have led to a number of remarkable
    rigidity type results both in von Neumann Algebras as well as Orbit
    Equivalence Ergodic Theory. I will highlight some of these results while
    paying special attention to applications with (amalgamated) free products
    of von Neumann algebras.
• Date: 10/16/06
  • no meeting, fall break
• Date: 10/23/06
  • Speaker: Adrian Ioana, UCLA
  • Title: Orbit inequivalent actions for groups containing a copy of F₂
  • Abstract: I will prove that if a group H admits a rigid action (e.g.
    H=F₂), then any group G containing a copy of H has uncountably many non
    orbit equivalent actions.
• Date: 10/30/06
  • Speaker: Ali Chamseddine, American University of Beirut
  • Title: Computational Methods in the Spectral Action Principle I
  • Abstract:
    In Einstein’s general theory of relativity the gravitational field is
    geometrical where the symmetry is diffeomorphism invariance and the dynamics
    is formulated in terms of the fluctuations of the metric. In noncommutative
    geometry diffeomorphism invariance is replaced with the spectral action
    principle which states that “The physical action depends only on the
    spectrum”. I review properties of noncommutative geometric spaces based on
    real spectral triples and explain the computational tools needed in the
    applications of this principle. As an example I will derive the inner
    fluctuations of the Dirac operator and show that for dimensions less than or
    equal to four one gets the sum of a Yang-Mills action and a Chern-Simons
    action.

• Date: 10/31/06 (Tuesday), NCG Seminar,
  4:10pm in SC 1432
  • Speaker: Ali Chamseddine, American University of Beirut
  • Title: Computational Methods in the Spectral Action Principle II

• Date: 11/2/06 (Thursday), Mathematics & Physics
  Colloquium, 4:00-5:00pm in SC 4327
  • Speaker: Ali Chamseddine, American University of Beirut
  • Title: Hidden Noncommutative Geometric Structure of Space-Time
  • Abstract:
    The geometry of space-time is reconstructed from the low-energy spectrum
    defined by the quarks and leptons. I show that there is a hidden
    noncommutative structure and that the dynamics of the unified geometrical
    theory is governed by the “Spectral Action Principle”.
• Date: 11/6/06
  • Speaker: Pinhas Grossman, Vanderbilt University
  • Title: Indices and angles for supertransitive intermediate
    subfactors
• Date: 11/13/06
  • Speaker: Akram Aldroubi, Vanderbilt University
  • Title: Slanted matrices, Banach frames, Wiener’s lemmas and
    inverse problems
  • Abstract: Click here for the abstract.
• Date: 11/20/06
  • no meeting, Thanksgiving break
• Date: 11/27/06
  • Speaker: Remus Nicoara, Vanderbilt University
  • Title: Subfactors and Hadamard Matrices
  • Abstract:
    To any complex Hadamard matrix H one associates a
    hyperfinite subfactor. The standard invariant of this subfactor
    captures certain symmetries of H. We present several classification
    results for Hadamard matrices and discuss some properties of the
    associated subfactors.
• Date: 11/30/06 (Thursday), Mathematics Colloquium, 4:10-5:00pm in SC 5211
  • Speaker: Sorin Popa, UCLA
  • Title: On the superrigidity
    of malleable actions
  • Abstract:
    I will present a series of results showing that measure preserving
    actions $\Gamma\curvearrowright X$ of countable non-amenable groups
    $\Gamma$ on a probability space $X$ that satisfy certain {\it
    malleability} and mixing conditions have very sharp rigidity
    properties. For instance, any cocycle for $\Gamma \curvearrowright
    X$ with values in a discrete group can be untwisted on the
    normalizer of any subgroup $H\subset \Gamma$ with the relative
    property (T). Same if $H$ is the centralizer of a subgroup $G\subset
    \Gamma$ on which the action has spectral gap. Bernoulli and Gaussian
    actions are typical examples of malleable actions. As a consequence
    it follows that if $\Gamma$ is either Kazhdan, is a product of two
    infinite groups, or has infinite center, then any Bernoulli action
    $\Gamma \curvearrowright X=X_0^\Gamma$ is {\it orbit equivalent
    superrigid}, i.e. if $\Lambda \curvearrowright Y$ is a free ergodic
    measure preserving action whose orbits coincide with the orbits of
    $\Gamma \curvearrowright X$ then $\Gamma \simeq \Lambda$ and the
    actions are conjugate.

• Date: 12/1/06 (Friday), Special Subfactor Seminar,
  3:10-4:30pm in SC 1308
  • Speaker: Sorin Popa, UCLA
  • Title: Rigidity phenomena from spectral gap and malleability
  • Abstract:
    I will explain a new strategy for proving rigidity
    results for II$_1$ factors, relying on the “tension” between
    a spectral gap condition (used in lieu of property T)
    and malleability. Applications include:
    a unique decomposition result for MdDuff factors;
    a primeness result for factors arising from Bernoulli actions of
    non-amenable groups; strong rigidity results for isomorphisms
    between group measure space factors $L^\infty X \rtimes \Gamma
    \simeq L^\infty Y \rtimes \Lambda$, with
    $\Gamma$ a product group and $\Lambda \curvearrowright Y$ Bernoulli.

• Date: 12/4/06
  • Speaker: Paramita Das, Vanderbilt University
  • Title: Relative commutants of depth two subfactors
  • Abstract:
    We show how Planar Algebra can be used to give a simple proof of the part
    of the Ocneanu-Szymanski theorem which asserts that for a finite index,
    depth two, irreducible subfactor $N \in M$, the relative commutants
    $N^{‘}\cap M_1$ and $M^{‘}\cap M_2$ admit mutually dual Kac algebra
    structures. In the hyperfinite case, the same techniques also prove the
    other part, namely that there is an action of $N^{‘}\cap M_1$ on $M$ with
    invariants $N$. This method extends to the general depth two case where
    the theorem had been generalized by Nikshych and Vainerman to obtain the
    structures of mutually dual `Weak Hopf C^* algebras’.