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Lundi 7 janvier 14:00-15:00 Pieter Spaas  (UC San Diego)
II_1 factors with a unique McDuff decomposition

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Lieu : Salle 2P8

Résumé : We consider McDuff decompositions of II_1 factors. In particular, we will discuss a structural result for such a decomposition when the central sequences of the non-McDuff part are captured by a Cartan subalgebra. We will also comment on some related properties and results for group actions and equivalence relations, in particular resolving a problem posed by Jones and Schmidt in 1985. Altogether these results will allow us to deduce several new instances of II_1 factors admitting a unique McDuff decomposition.

II_1 factors with a unique McDuff decomposition  Version PDF

Lundi 10 décembre 2018 14:00-15:00 Thiebout Delabie  (Université Paris-Sud)
Geometric Property (T)

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Lieu : Salle 2P8

Résumé : Box spaces are metric spaces created using a group and a sequence of finite index normal subgroups. There are many relations between the properties of the box space and properties of the group that was used to create them. Most notably, Margulis showed that box spaces of groups with property (T) are expanders. However not all box spaces that are expanders are created by a group with property (T).
So being an expander does not tell you if a box space was created using a group with property (T), but there exists a property that does. In 2013 Willett and Yu introduced geometric property (T) and showed that a box space has geometric property (T) if and only if the group has property (T).

Geometric Property (T)  Version PDF