Free probability seminar

Talk

Speaker: Claus Köstler
Affiliation: St. Lawrence University
Time and Place: Wednesday, October 8, 2:00-2:55pm, Milner 216.

De Finetti theorems in noncommutative probability

Distributional symmetries and invariance principles of sequences of random variables lead to deep structural results in probability theory. For example, exchangeability means that the joint distributions of a sequence is invariant under finite permutations of the random variables. Now the classical de Finetti's theorem characterizes exchangeable infinite sequences to be conditionally i.i.d. A natural question is to ask for noncommutative versions of this fundamental result. I will report on recent progress in this matter.

A very recent result is the free version of de Finetti's theorem, obtained in joint work with Roland Speicher. Replacing the role of permutations by quantum permutations we obtain a new characterization of Voiculescu's freeness with amalgamation.

Also, I will present a more general noncommutative version of de Finetti's theorem where conditional independence emerges in terms of commuting squares of von Neumann algebras. Finally, if time permits, I will address results on braidability, a new symmetry recently introduced by Rolf Gohm and the speaker.


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