## John-von-Neumann-Lecture: Prof. Dr. Sorin Popa, University of California, Los Angeles, Vortrag: Structure and randomness in von Neumann algebras

### am 04.05.2017 um 16:30h im Raum M5

Abstract: von Neumann algebras are non-commutative versions of the function algebra $L^\infty([0,1])$, the same way matrix algebras $M_{n\times n}(\mathbb C)$ are analogue to finite spaces. A particularly important class, called II$_1$ {\it factors}, arise as infinite tensor products and ultra products of matrix algebras, and also from groups $\Gamma$ and their measure preserving ergodic actions on probability spaces $\Gamma \curvearrowright X$. A key analysis tool to study II$_1$ factors is {\it deformation-rigidity theory}, which exploits the tension between ``soft'' and ``rigid'' parts of the algebra to unravel its building data. This fits within the fundamental dichotomy {\it structure versus randomness}, which appeared in many areas of mathematics in recent years. I will present several rigidity results obtained through this technique, showing for instance that II$_1$ factors arising from Bernoulli actions of property (T) groups $\Gamma \curvearrowright X$ ``remember'' both the group and the action, and that free ergodic actions of the free groups $\Bbb F_n$ remember the rank $n$.

Angelegt am 11.04.2017 09:15:52 von

Geändert am 18.04.2017 09:00:46 von

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Kolloquium der Mathematischen Institute (unterstützt durch den SFB 878)

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