# Séminaires : Séminaire d'Algèbres d'Opérateurs

 Equipe(s) : ao, Responsables : François Le Maître et Romain Tessera Email des responsables : Salle : 2015 Adresse : Sophie Germain Description

 Orateur(s) Sorin Popa - Fondation des Sciences Mathématiques de Paris et Fondation Hadamard, Titre On the vanishing cohomology problem for cocycle actions of groups on II_1 factors Date 21/06/2018 Horaire 11:00 à 12:30 Résume I will present a result showing that any free cocycle action of a countable amenable group $\Gamma$ on any II$_1$ factor $N$ can be perturbed by inner automorphisms to a genuine action. Besides containing all amenable groups, this \it vanishing cohomology property, called $\Cal V\Cal C$, is also closed to free products with amalgamation over finite groups. While no other examples of $\Cal V\Cal C$-groups are known, by considering special cocycle actions $\Gamma \curvearrowright N$ in the case $N=R$, $N=L(\Bbb F_\infty)$, one can be exclude many groups from being $\Cal V\Cal C$. I will also explain a connection between the vanishing cohomology problem and Connes’ Approximate Embedding conjecture. Salle 2015 Adresse Sophie Germain